Can someone explain the concept of animating bitmaps to me.

Question

What I want to do is take my rpg man sprite and understand how I can access each of his eight animations with methods. I've looked at code that does something like this but I'm not quite getting it. Right now, I got my guy to do two seperate animations from two separate bmps and he's facing forward in every direction he goes.So it looks like he's walking forward all the time. I guess what I am asking is how do I go about accessing all eight of his animations from a single bmp and assign them to the direction I want that animation to go to?