If you are on keyboard, it can be kind of annoying to have all of your controls in xbox format (I don't know how to turn that off) Anyways, some moves are behind a swooping motion on the dpad, like the final flash Super Saiyan Vegeta has. This is all on the default control scheme, so if you've re-mapped your controls then I would just look up the default controls.

Super 1: Just the "I" Combo

Super 2: Hold the button you have set to down and the directional key opposite to the way the enemy is on your screen, then press P or the ; key, for example, if I wanted to use final flash, and my opponent was on the right side of the screen, I would press S> then A quickly after, then P or ; after.
In short: S>A> P or :
I figured this out by pressing buttons randomly based on what was given to me in the combo list in training. Thank you developeers for thinking about the Keyboard players. To clarify, this does work on other characters, I know there is a button input mapping thing in the lobby. I was confused about how to actually use my 2nd supers for the first 8 hours I have played the game, just want to put this out for people who are also confused, I might not be the first person to do this, but if I am I think it's important that people know how to deal damage in the game.
Other combo I figured out randomly: (enemy on right) S+A and U+K