"The women have to enter the gallery."
Translation:Las mujeres tienen que entrar a la galería.
'a' is a preposition and it does not have a direct translation. It basically means 'at' or 'to', but it doesn't perfect translate. There are several functions of using it, and you will start to get them more easily with practice.
I believe everyone understands that "a" means "to." The question is why in the sentence, "The women have to enter the gallery" why is it necessary to say ...have to enter TO the gallery when the sentence already has "to enter" in it?