Class A technical fouls involve either unsportsmanlike conduct (arguing with the officials, taunting the opposition, etc.) or contact with an opponent (shoving, for example). This results in the standard two shots and counts as both a personal foul for the player (assuming the technical wasn't given to a coach) and a team foul for the team. Get charged with two class A technical fouls in a game and you're ejected.
Class B technicals involve neither unsportsmanlike conduct nor contact with the opponent. Hanging on the rim (which one could argue is unsportsmanlike, but by the rule is not) is the most common way to get this. There are also a couple of ways to get a warning, delay of game and flopping being two. Essentially, if a team accrues two warnings in a game (or two infractions that would lead to a warning), the individual responsible for the second infraction is assessed a class B technical foul. The penalty for that is one foul shot, and no personal foul or team foul is charged. If an individual gets charged with either three class B technicals or one class A and two class B, though, then they're ejected. Additional warnable infractions after the second result in additional class B technical fouls.
So, Florida State had already been warned for delay of game after they touched the ball instead of letting us pick it up to inbound after a made basket. They were then charged for flopping, which was their second warnable infraction, meaning they were charged a class B technical.
There are also "administrative" technical fouls, the penalty for which is similar to a class B (one shot, no team foul) and is given for things like having six players on the floor, calling a timeout when you don't have any, not filling the scorebook out properly, equipment infractions, etc.