The basic idea is to separate the Autofocus function from the shutter release function by assigning each function to a separate button. Press one button to focus, press the other to snap the shot. Once you've pressed the autofocus button, the the focus is set and will hold there as long as you like (and you don't need to hold the button down). You can continually hit the shutter release button as many times as you like after that without worrying about the camera re-autofocusing again, potentially on some other object that you didn't intend.
I used to use the AF-L/AE-L button a lot to lock the focus so it didn't go hunting for focus again while I took my shots, but that required holding the button down. Now I just hit the button once while targeting my focus, and then I'm free to re-compose my shot without worrying about keeping the focus point on target.
Oh and hi-five to a fellow D7000 owner.