Upload & Sell: On
Just give it a try, you'll immediately see how each work. Looking through the viewfinder while doing this will show whether AE lock is on/off. This is the beauty of digital, you can experiment and get immediate feedback.
Generally you would meter to taste, lock it, focus with your back botton and shoot (or back button focus on static subject, release (so your subject in focus stays in focus), recompose and shoot. Obviously as part of your metering you are going to pick the aperture, speed, and iso that's desirable. The combinations are many depending on what you are shooting and your objective (sports, model, landscape, wildlife, architecture, ...)
Oh, toss in a flash or three and it gets even more interesting