It’s a word to link nouns,pronouns or just other phrases.
Some examples of using a preposition are:
simple prepositions:
He sat on the chair
He drank milk
double prepositions:
The baby climbed on the table
She never leaves without her phone
Compound:
She sat beside Marie
My dog ran track with me
Participle preposition:
She is interested in anything concerning horses
Phrase preposition:
The baseball game was cancelled because of the rain
You can basically use them by showing location,time,direction, cause and possession.