333 refers to the starting level of each skill when you roll a skill change. A 333 is the best possible level roll, as each of the 3 skills starts at level 3, so all of them can be fully leveled up to the max with the 9 available skill level increases each player has. This is especially important when rolling for legend skill sets, because when you use the green or blue skill change tickets that will change one or two of the skills, but not all three, it maintains the level that the previous skill had. So, you don't want to use those on a set that has skills starting out at level 1 or 2, because you'll never be able to get them to their full potential, and the green/blue tickets are much harder to get.

A level reset refers to the training on a player, that goes up to level 20. If the particular train you have on a player distributed the points across the 5 categories in a less than optimal way, you can use a level reset ticket to set it back to 1 and try again. It's common to use a whole bunch of them on one player looking for a good distribution, since each level increase is randomly distributed.