There's an entire playlist on youtube for this game that has TONS of useful information. A lot of these videos are older, but I'll assume what's talked about is in this present version in 1 form or another. I'll point out answers to a lot of things I had no idea about.

HOW TO WIN (bold statement):
*** https://youtu.be/soAV0Qi-LTc?t=1767

Trading:
*** What are other teams' weaknesses and their plans? https://youtu.be/anOOI0clRY8?t=249
******** "Under the hood". https://youtu.be/XAvo_dXt-Cc?t=887
*** How many years are left on contracts? https://youtu.be/anOOI0clRY8?t=442
*** "Under the hood" of AI trading. https://youtu.be/anOOI0clRY8?t=545
*** "Under the hood" of AI draft pick trading. https://youtu.be/anOOI0clRY8?t=1608
*** What does the orange "get offer" button in the upper right do? https://youtu.be/XAvo_dXt-Cc?t=1083 /// https://youtu.be/7gA__vV3IZA?t=857
******** Checking 1 team at a time is intentional. https://youtu.be/ugVWeheewdU?t=565
*** During off-season free agency, full financial modes, I think; sign & trade. https://youtu.be/1BxbJf3By9o?t=1423 /// https://youtu.be/FFW2sEdmXcU?t=1063 /// https://youtu.be/GhKEGi7zSLQ?t=2314
*** How the trade block works: https://youtu.be/FFW2sEdmXcU?t=886
******** media stories generated and players' attitudes might change. https://youtu.be/FFW2sEdmXcU?t=1004
*** Red "clear trade" button (right side of screen) and general discussion. https://youtu.be/ugVWeheewdU?t=368
*** AI trades more as you approach the deadline. https://youtu.be/ugVWeheewdU?t=681

Drafting:
*** Addressing he "there's not enough talent" complaint. There are rare "boom" and "bust" prospects. https://youtu.be/anOOI0clRY8?t=1394
*** What is the "league media" tab (upper left) -> "draft picks" tab (upper right) for? https://youtu.be/anOOI0clRY8?t=1742 /// https://youtu.be/GhKEGi7zSLQ?t=1778
*** "pre-draft workout" screen and the draft board. https://youtu.be/sA7_7jANU_o?t=340
*** On the main draft screen, you know the bubbles that show each announcer's speech? https://youtu.be/5MSzrN02DS0?t=1788 /// If you hover your mouse on a bubble, that bubble will stay on the screen, so you can read all the text. The bubbles disappear too quickly for me otherwise.
*** What is the way to look at the history of all the previous drafts? https://youtu.be/4gjy2TsTx34?t=571

Staff:
*** What do the ratings mean? Assistant coaches are important, too. https://youtu.be/XAvo_dXt-Cc?t=209
******** Only the head coach's game strategy rating is used, not yours or any of the assistants. https://youtu.be/XAvo_dXt-Cc?t=332
******** player development. https://youtu.be/XAvo_dXt-Cc?t=385
*** Which head coaches MIGHT accept demotions: https://youtu.be/ovecNLAQE54?t=882

Free agency screen (during the free agency portion of the off-season):
*** What does the "show target players only" checkbox (upper left) do? https://youtu.be/XAvo_dXt-Cc?t=1212
*** The 3 green tabs at the top right and a tactic with the "advance 1 day" tab: https://youtu.be/ugVWeheewdU?t=1198
*** The orange "latest rumors" button (upper left): https://youtu.be/1BxbJf3By9o?t=1003
*** In your email, on June 28, you get free agency evaluation. Look out for friendships in the "misc" line of each player. https://youtu.be/M5QONoC1mA0?t=1533

Insights tab (lower left)
*** Tracking cosmic level stats https://youtu.be/FFW2sEdmXcU?t=142 // https://youtu.be/4gjy2TsTx34?t=1582 /// https://youtu.be/GhKEGi7zSLQ?t=1490

AI
*** The staff - making excellent personnel decisions to poor. Quality of AI trading discussed: https://youtu.be/7gA__vV3IZA?t=377

Depth chart
*** How to use it. This chart is pre-DDS 2021, but the ideas are sound: https://youtu.be/FFW2sEdmXcU?t=1289
*** Explanations of almost everything (sub-out and actually how to move players not mentioned): https://youtu.be/7gA__vV3IZA?t=1042

D or G league (same thing)
*** How to use it: https://youtu.be/soAV0Qi-LTc?t=226
*** two-way players (2W): https://youtu.be/soAV0Qi-LTc?t=525
*** Effects on players' development: https://youtu.be/soAV0Qi-LTc?t=670
*** D league changes and DBL select players: https://youtu.be/5MSzrN02DS0?t=244 /// https://youtu.be/GhKEGi7zSLQ?t=887
******** after a bunch of games are played: https://youtu.be/5MSzrN02DS0?t=976
*** Depth chart. You can make draft picks, for example, get maximum minutes so they develop as quickly as possible (by D-league standards): https://youtu.be/7gA__vV3IZA?t=1578
*** Roster. https://youtu.be/7gA__vV3IZA?t=1652 /// https://youtu.be/ugVWeheewdU?t=244

"League Media":
*** "daily news" and "season news" tabs, how can I see the player the slice is referring to? https://youtu.be/XAvo_dXt-Cc?t=564
******** Use these news screens for trade rumors, "shopping player" rumors, team conflicts. https://youtu.be/1BxbJf3By9o?t=1292
*** Daily and season goings-on. https://youtu.be/ugVWeheewdU?t=950
*** "magazines" tab, "view free agency guide" (2nd magazine). Tactic on increasing chances of getting a particular free agent: https://youtu.be/M5QONoC1mA0?t=1094

Players' personalities and ratings
*** Can I keep a player for his whole career? "Loyalty", "greed" and "play for winner" mentioned https://youtu.be/soAV0Qi-LTc?t=1614
********* "play for winner" very important for great players. https://youtu.be/GhKEGi7zSLQ?t=2939
*** What to do if you want a player to change his style of play and the limited success you MIGHT have: https://youtu.be/soAV0Qi-LTc?t=1973
*** overall and potential ratings commentary. https://youtu.be/4gjy2TsTx34?t=749
*** coach, team, and organization relationships bars; phone usage for problems with players and coaches; https://youtu.be/GhKEGi7zSLQ?t=2806 /// https://youtu.be/GhKEGi7zSLQ?t=3081
*** relationships effect(s) while the player is actually playing. https://youtu.be/GhKEGi7zSLQ?t=3161

Player cards
*** overview: https://youtu.be/GhKEGi7zSLQ?t=1181

Player types
*** Some explanation: https://youtu.be/soAV0Qi-LTc?t=1330 // https://youtu.be/4gjy2TsTx34?t=683
*** Players can gain and lose their icons. https://youtu.be/GhKEGi7zSLQ?t=1364

The college game (2020 and 2021 versions) and this game.
*** Why should I purchase it and integrating both. https://youtu.be/sA7_7jANU_o?t=766 /// https://youtu.be/1BxbJf3By9o?t=293 /// https://youtu.be/FFW2sEdmXcU?t=1570 /// https://youtu.be/GhKEGi7zSLQ?t=554

Built-in note taking:
*** Can be used to keep track of players. https://youtu.be/sA7_7jANU_o?t=1539

"Schedule" tab (lower left)
*** What does this do for me? https://youtu.be/soAV0Qi-LTc?t=459

Milestones
*** What are they? https://youtu.be/4gjy2TsTx34?t=335
*** Where is the tab to look at all of them? At the left. Usage shown. https://youtu.be/ovecNLAQE54?t=225

Transactions screen.
*** https://youtu.be/ugVWeheewdU?t=824

History page (bottom left of screen).
*** What's happened to your team as the years passed? https://youtu.be/ugVWeheewdU?t=1043

Game options screen (upper left corner, the "hamburger" menu).
*** This is where you set the AI to handle portions of your team(s). The "pace adjustment" combo box is detailed. https://youtu.be/ugVWeheewdU?t=1359

Training camp screen
*** What do the sliders do? https://youtu.be/GhKEGi7zSLQ?t=2598
*** What is the white screen at the end of training camp? https://youtu.be/GhKEGi7zSLQ?t=2681

Dashboard screen
*** Details. https://youtu.be/GhKEGi7zSLQ?t=1089

On play/sim screen, aka, daily schedule screen
*** How to sim to a certain date: https://youtu.be/M5QONoC1mA0?t=352
*** Game preview icons https://youtu.be/GhKEGi7zSLQ?t=1588

This post should totally be stickied or something.

Thanks for doing this! Definitely going to stick this here for everyone else to see!

Cool.

How to delete old saves
*** Verbal description only, nothing shown on this. https://youtu.be/M5QONoC1mA0?t=1250

Summer league
*** What were each players' stats? Email has best players. https://youtu.be/M5QONoC1mA0?t=1281

Universe mode (after you select "new league" on the opening screen menu)
*** Single player mode where you can control 2 or more teams. https://youtu.be/GhKEGi7zSLQ?t=215

"Database editing" (1 from the bottom of the opening menu)
*** How do you permanently change team(s) colors, number of teams, and such? https://youtu.be/GhKEGi7zSLQ?t=498

Injuries
*** How can I get injuries during the summer? https://youtu.be/soAV0Qi-LTc?t=1155

2D (watch or play a game):
*** How to get "play-by-play" versus "recent plays" and what they are. https://youtu.be/XAvo_dXt-Cc?t=1625
*** Handling players in foul trouble, both manually and the AI. "int" rating of player comes into play. https://youtu.be/ovecNLAQE54?t=945

HTML.
*** For box scores and player cards outside the game. Useful for multiplayer, but single player can use, too: https://youtu.be/ugVWeheewdU?t=1537

Manually adding or editing a player
*** Where do you do this? You can edit players here, too. https://youtu.be/1BxbJf3By9o?t=1210

Editing or adding coaches
*** https://youtu.be/YYqMeF8kV90?t=969

Expansion teams
*** Commentary https://youtu.be/v8xR9p0yEfg?t=1659