deartháir a brother

An This verbal particle before a verb indicates a question
just as Ní indicates the negative

An bhfuil ..... agat Do (you) have ..... ?
This is the interogative form of tá... agam I have.
The negative is níl ... agam I do not have.
Níl is really an abreviation of ní fhuil
which is never written now but keeping it in mind
will improve your pronunciation of this word.
The two elements should be heard in speech