accessing the same email from multiple computers

Hi

can people suggest the best way to set my email up so that no matter whether I check it on my macbook air, imac or even on the web, I won't get loads of unread messages even though I have read them? Ideally I'd like it so that eg I check mail on my imac and read everything, then when I check later on my macbook, only new stuff will appear and things I've already read will show up as already read.

I have a couple of gmail accounts and a standard email account with my isp.

Do i need to learn how to setup IMAP? Its all very confusing and not somethign I've looked at before.

How does it handle folders? Eg if I archive stuff to folders for storage. Thats offline but can it show those? I don't mind if they have to be stored on the one computer, just wondering