A preposition is a word used to link the noun or pronoun with other words in a sentence. There are three types of preposition: They can include time, place or direction. 

EXAMPLES

Trabajo a las nueve – I work at nine.

Salen del colegio a las cuatro – they leave school at four.

El perro está cerca de los niños – the dog is near to the children.

Los flores están sobre la mesa – the flowers are on the table.

El autobús va hacía la ciudad – the bus goes towards the city.

El colegio está cerca de su casa – the school is near to his house.