Any ability listed on your page that you have Active will be in BOLD. If an ability is not activated, you cannot use it. Each time you level up/down, you get a chance to reallocate your EXP. You have 1 EXP per level, and the EXP you have is always equal to your current level. Unlocking an ability does not mean it is necessarily unlocked permanently. Therefore, sometimes you must drop abilities to get others.
2 options exist for abilities that are not overt – 1) ways to get extra EXP, 2) 2nd and 3rd level abilities.
VICES are purely negative abilities you can take on (voluntarily or otherwise) that cost -EXP, meaning they free up EXP to spend elsewhere.
Many (but not all) abilities have multiple stages, which have stronger variants at greater costs. Each successive stage will cost 2x the value of the next, and the highest stage is typically stage III. Higher stage abilities are not only better, but are also more difficult to remove using certain abilities. Example: Weaponized Body I/II/III – Cost 2/4/8 exp respectively, and boost bodily damage by 1.5x/2x/3x respectively.