Can someone explain ContextActionService?

Hi, I'm wanting to create a system (where you can unlock keypress abilities depending on your level/currency) in the future, and from what I've learnt so far is that ContextActionService would be better than UserInputService for this sort of thing, however I'm really not sure has CAS functions (more importantly binding and unbinding functions), what the parameters are, how I call it etc. I've read up on the wiki and watched some youtube videos but I'm still unsure of how it works. Any explanations or help would be appreciated.