Don't panic - it's all relative. Everything you know already will be as you expect. It'll just sound lower.
Some of us keep our banjos in what we call "A" tuning so what you think of as a C chord would sound like an A . Your G would be an E and so on.
Some folks keep our banjos even lower in "G" tuning so your C chord would sound like a G and your G like a D etc.
Hope this helps