"Do you have shoes?"
Translation:An bhfuil bróga agat?
No. An is the question form of is, the copula, which is used in classification and identification sentences (there are other, more advanced uses). An can also be a question particle used before other verbs, too. So in this case you need the correct form of bí, since it's not an identification or classification sentence.
Bí by itself means the same thing as English's be. There are a lot of prepositions that can be used with bí in order to change: bí ag for have, bí ó for want, bí ar for have (emotions, conditions, and more but not possession), bí faoi for intend. There are probably others that I can't think of right now.