This is way to general. You won't get an answer to this one.

Most preposition have a fixed context to use eg, 'on' for day of the week (on saturday), 'at' for time (at 3 o'clock), others are pegged to a verb. All of these require memorization although similarities between verbs help to distinguish which preposition is to be used.

I think we would need examples of what you are trying to learn for this to be explained :)

That's really complicated.