Is 'they' a verb or a noun?

The word 'they' is not a noun or a verb; 'they' is a pronoun, a word that replaces a noun. The pronoun 'they' is used for the subject of a sentence and the pronoun 'them' is used for the object of the sentence. Examples:

They are my friends. I go to school with them. (they and them are replacing the noun friends)