I'll give you a few of the main uses of these prepositions:
For movement from one place to another : Let's go to the beach
Grammatically, as part of the infinitive : I want to learn English
For times on the clock : at midnight, at 10 o'clock, at 11.30
To indicate a location (no movement) : I am at the cinema
For a length of time: I've lived in London for 5 years
Also in phrases like: These flowers are for my mother
To mean near or next to: She lives by a lake
To describe a means or method: We went by car
As an agent in a passive construction: The poem was written by Shakespeare.
There are other uses of these prepositions, but these are some of the commonest ones. The important thing for you to remember is this:
Don't try to translate prepositions directly between Spanish and English!
You should try to learn short simple phrases in English (such as 'Let's go to the beach!' above). This will fix in your mind the way we construct sentences in in English. When we learn our mother tongue, we all learn simple phrases in context rather than single words, and that's the best way to learn a foreign language, too. You can't always translate prepositions, and you shouldn't try to.
I hope that helps. Do please ask again if you have any specific questions about how we use 'at' or any of the other words.