Let me break it down a little further.
The 722 has two satellite tuners and an off the air tuner. If you get an off the air digital signal from your locals, you can tune three channels at once.
The 722 has a hard drive. The program on each of those three channels can be recorded to the hard drive simultaneously.
The 722 has two banks of outputs, one bank able to output HD and the other is able to output SD. Generally, these are referred to as TV1 and TV2.
The 722 operates in two modes.
One of those modes uses only TV1 outputs. If that is the mode you decide to use, then you can record something on one satellite tuner and something from the OTA tuner and watch the other satellite tuner. It varies in combination, but you cannot have all the tuners recording and watch something live, but you can watch something recorded.
In the other mode the system uses both TV1 and TV2 outputs. They use different remotes. And one satellite tuner "belongs" to each. If your satellite tuner is recording, you can't watch satellite TV live. But you can watch any recording on the drive recorded by any tuner.
Obviously there are more complications than this, but that's the basics. It's all about three tuners, a hard drive, and two sets of outputs. They just happen to be in one box connected by computer circuitry.