Asyou know, there are several kinds of prepositions: prepositions of time, prepositions of place, prepositions that follow certain verbs, prepositions that follow certain adjectives, etc.
Let's take this picture as an inntroduction to the topic and from here we'll study the different prepositions separatly according to the group they belong to.
Now, "in, on, at" are the three most important prepositions in English. They can refer to either time or place. Their use is quite tricky, especially for Spanish students of English.You may want to have a look at the picture below. It provides you with a general idea of what these prepositions are used for.
On a different note, verbs can also be followed by prepositions. Have a look at the following picture.









