When is them used in a sentence?

Answer 1

Them would be used as an adverb:

I like them.

I gave them a stone.

Them would not be used like this:

Them apples were good.

I like them bananas.

Answer 2

"Them" is typically used as a pronoun to refer to a group of people or things that have already been mentioned or are known from context. It is often used when the specific individuals in the group are not the main focus of the conversation.