A preposition is a word that connects words and creates a relationship between them.
Preposition Uses:
1) Preposition + noun:
Contra mi auto / against my car
Sin dinero / without money
2) Preposition + pronoun:
Para mí / for me
Entre nosotros / among us
3) Preposition + infinitive:
Sin comer / without eating
4) Verb + Preposition:
Viniendo de lejos / coming from far away
Voy hacia la locura / I am going crazy