Do you know the dimensions of the tank e.g. 1ft high x 2ft wide x 2ft deep ?
Leopard gecko's are usually the best first reptiles as they are easy to care for and don't cost much to keep but they're also really cool and pretty
I've got a care sheet on my website that tells you everything you need to know about leopard gecko's and there are some other care sheets on there as well about bearded dragons and other bigger lizards.
PM me if you want to know anything else. I know a little bit about tortoises as well