There's a lot of drama but basically:

There are five main (Power Five) conferences in NCAA football: the Southeastern Conference (SEC), the Big Ten, the Big 12, the Pac-12, and the Atlantic Coast Conference (ACC). ESPN has an unofficial thing where an SEC team has to be in the final four for purposes but prior to today an undefeated Power Five (P5) champion has never been denied a spot in the final four. The final four do a normal playoff for the National Championship.

Michigan (part of the Big Ten conference) cheated to get to #1 by stealing signs all season (the coach is fired and being investigated) but they were undefeated and won their conference.

Washington (Pac-12) was also undefeated and won their championship and they made it in. Also the Pac-12 was deliberately low-balled by media companies for the past few years in order to destroy the conference and next year every team is going to leave the conference. for the Pac-12

Texas (Big-12) and Alabama (SEC) won their conference and only lost one game all season. The game that Alabama lost, however was against Texas (There are interconference games). Because of this the commissioners (13 people who choose the college football rankings) have been putting Texas above Alabama all season. Next year Texas is moving to the SEC.

Florida State (ACC) went undefeated and won their conference. Yet they were snubbed a final four spot. The commissioner's logic is because FSU's star quarterback broke his leg a few weeks ago (in one of the gnarliest live moments on TV. literally it looks like he has a second knee) and their second string quarterback had a concussion and was out for the ACC championship. FSU still won the ACC championship with their third string and their second would be back by the playoffs

tl;dr hoes mad