Bhfuil is a special form of tá that's only used after certain words, such as an. Without the words that trigger this change, you would just have tá.
The other thing is that you need an .. ? to form a question. You can't just say tá cáca agat? and change your tone to voice to make a question, as in English. You need to do an + tá cáca agat = an bhfuil cáca agat?.
Fun fact: "caca" (with out accent) in spanish means "poop". I'll always lugh with that, I would never be able to say 'ithim cáca" without thinking that I'm saying "Como caca" ("I eat poop")