A prepositional phrase is made up of a preposition and a noun phrase. We use prepositional phrases for many purposes, for example:
We will be back in a few days.
They drove to Glasgow
Helen is the girl in the red dress
The lion was killed by the hunter
I saw a wonderful painting by Van Gogh
We gave five pounds to the woman on the corner.
They got a drink for me.
The book belongs to me.
I had an argument with my brother.
I feel sorry for you.