Thanks everyone for your help. My dad was gave me his train set and I figure I need some upgrading.

So if im going to purchase a diesel loco. then I dont need to worry about 0-6-0 or another set of numbers. Just the steam loco?

I am very interested in getting into this hobby. But Im unclear on what they mean by 0-6-0 or 4-8-4 when purchasing a locomotive. Can anyone help?