Hi guys - you'll soon see why I posted here - real newbie question!

I've been happily using a workgroup network for a while now.
I'd had seven windows PCs in one building cabled together and working happily.

Now I'd like to network some PCs that are located in another building.
Am I correct in thinking that I need a 'domain' based network?

I've just started using Ubuntu Linux and have a server running Apache & MySQL - it seems to be working ok.

Will a domain based network allow my other users to access the network from their remote location?

I have been searching various strings on the net like....

domain based network linux tutorial
linux domain network tutorial

...and soooooooooo many more - but I can't find any such tutorial to get me going.
Actually, one such search lead me here.

If anyone has any advice, please help

Many thanks,