gecko_

I am new to this site so I have no idea how it works. But, I will soon be getting a leopard gecko just as a pet and I wont be breeding or doing anything like that. I have a 20-gallon long and I have been told I can house 2 leopard geckos in it. I just want to go to Petsmart and get 1 leopard gecko to start and was wondering if anyone had any ideas so I can make sure I get a female so I can add another female later on.