Do I need to get two sticks of RAM to get into dual-channel mode?

First of all, what exactly does dual-channel mode mean? I'm trying to put together all the parts needed to build a new PC and it just occurred to me that if I buy only one 8GB stick of RAM, then I wont be able to have the dual-channel mode going on, or will I? Is it imperative to have two sticks of memory installed to get this dual-channel mode? Or does RAM these days have some feature that if you're only using one stick, that it emulates dual-channel mode? That's seems like a far-fetched concept but I have to ask. So, if I can't get dual-channel mode using just one stick, then I'm going to have to use two sticks of 4GB memory to make this work, in which case I'll have to start shopping around for deals on 4GB sticks now. Thanks for any and all info you can provide me!