[Build Help] How do I move my OS to my new SSD?

I just bought a Sandisk Ultra II SSD for my first build I plan on building soon. I am wondering how I am supposed to move just my OS to my SSD while keeping everything else on my HDD that I'm currently using. Iv'e done some research but can't find a clear-cut answer. Some sources say that I need an external drive (that I don't own) Others say I don't. I would love to have to fast boot times everyone is talking about. Thanks for helping a PC building noob out! :)

EDIT: I am using Windows 8.1 right now. If that matters. If it wasn't clear before, I am planning on using both my old HDD and new SSD on my new computer.

EDIT 2: Sorry if I seem like an idiot to this stuff. Computer software is not my forte.