Your sublcass levels up like anything else; by finding things, doing missions or completing quests. Just like in every other game. What is different, however, is how you unlock the skills within the subclass. There is no control over unlocking certain abilities. Rather, it upgrades down the row. After you gain enough exp, you will unlock the next ability in the row you are currently leveling. After you unlock one ability in a column, you start gaining exp towards the next ability in the column. However, it is spaced out so that you will not unlock an ability on the 2nd row until all abilities in the 1st row are unlocked. Meaning that you will gain all abilities in the order they are in from left to right. As for the experience itself, I do not fully understand how it is split, but from what I could gather, the amount of exp you get from each action is given equally into all of the skills you can currently put exp into. If you have unlocked 4 abilities on the first row, then exp will go into the 5th ability on the same row, as well as the first 4 abilities on the 2nd row. Whether the exp is split between them or each gets exp equal to that of what was gained, I do not know, however I'm willing to bet on the latter (as skills did not seem to level slower just because you were unlocking more of them) There is no easy way to get work towards your later jump or grenade skills. You just have to get every ability that comes before them. Though if the beta is anything to go by, you should have those unlocked in your first subclass by around level 10 or 11. Keep in mind that if you choose a 2nd subclass, you will have to unlock all of these skills over again.