1. Used at the beginning of a sign sentence to mean the acton in that sentence is done for no particular reason, or just for the sake of it, e.g., for amusement or fun, or because you can see no reason why not to do it. English = "Why not?!", "Just for the sake of it," "Just for the hell of it."
2. Used to introduce something or between the mention of two things to mean that the thing you introduce, or the two things you mention, are roughly like some other thing or each other. English = say (i.e., "for instance"), for example.
3. Used at the beginning of a sign sentence to mean that the action in that sentence is not real or actual, but you are going to pretend it is and see what that means. The situation you imagine is usually positive. You know a past action did not happen, a current action is not happening, or a future action has not happened yet, but you talk about it anyway. English = if.