Prepositions describe the location of one object in relation with another object (The pen is on the table)
We use prepositions to say time phrases. (Her birthday is in August)
We use prepositions in phrasal verbs (The plane takes off at 2pm)
We use prepositions in phrases. (We have many books in stock)
We use prepositions in idioms (He was over the moon with his great results!)
We use prepositions with some verbs / adjectives / nouns. (She succeeded in passing the test / She was successful in passing the test / She had great success in passing the test)
If we use a verb after a preposition, we normally put the verb in +ing form. (After going to the cinema, we ate in a restaurant)