Older cameras (like the 40D) have two AF point selection modes, automatic and manual. The 7D has five, so another way of selecting them had to be designed.
You select AF point selection mode by pressing the AF point button on the rear, then cycle through those you've enabled with M-Fn.
Once you've selected a method, you can then select which point within that method by pressing the AF point selection button on the rear, and then use main dial, quick dial or joystick.
Or you can use Custom Function IV-1 to set the rear dial and/or the joystick to make such a selection directly, without pressing the AF point selection button first.
You can select to have the AF points light up in red always, only when it's dark outside or never. If you don't want them to light up, you'll still see them in black in the viewfinder.
You can also select to see all points, including those not used, in the viewfinder. Or only those you actually use.
When using Servo AF with multiple points, you can select to see which are active, or not see them at all.
When selecting a single point, you can select that the camera will stop at the edge of the AF point pattern, or wrap around from the left side to the right, for example.
When holding the camera... Well, I think I better stop here. This list would be at least twice as long, before all the settings and customizations of the 7D's autofocus system have been mentioned.
There are many more AF-related settings on the 7D than you'll find on the 40D. Several things are done in a different way, compared to the 40D.
Some things are pretty complex, like having the whole AF mode selection and optimization settings changed by just holding a button, and then back when releasing it, and all this adapting to how you hold the camera (horizontal/vertical) automatically!