How exactly does a holding deposit on an apartment work?

The apartment we fell in love with and approved for won't be ready until oct 1st. She said we can put a hundred down when we spoke on friday and she would give us a call this week to set up the agreement and deposit. That deposit will hold the apartment for us. I really want this place I dnt want anybody to take it :( can they decide to give somone else the apartment after we give them the deposit? We have the money and are ready!!! Just a worry a guess lol|||You give deposit. They hold unit (stop showing it to other prosepctive tenants). if you back out, you lose said deposit.