The Digidesign DigiRack Signal Generator is a free piece of software that comes stock in all versions of Pro Tools. I've used it both with Pro Tools 7 and 8, but believe it can be found in earlier versions as well. You don't have to install it, as it will be taken care of during the process of installing Pro Tools. In terms of the interface, it's straight forward as it simply has parameters for setting the frequency, the level, and the type of wave that you'd like to hear. You can also choose between either peak or RMS. It's a compact interface, but it's really all that you need for a signal generator. A manual isn't necessary under any circumstances - if you are confused I'd just do a Google search on signal generators.
I'm running Digidesign's DigiRack Signal Generator right now in Pro Tools LE 8. I've also used it in Pro Tools 7.4 LE and HD. At home with Pro Tools 8 I run it on a Mac Book Pro that has a 2.2 Ghz Intel Core 2 Duo processor and 4 GB of RAM. I run Pro Tools LE 8 with a Digi 002R audio interface or a Digidesign Micro Box if I'm on the move. In both Pro Tools LE and HD, I've been able to run a signal generator on 24 tracks without a problem to test the system. I can't imagine that too many users will have a problem running this as long as you can currently run Pro Tools with some plug-ins without a problem. If you have Pro Tools, you can test it out on your system for yourself.
It's definitely nice to have the Digidesign DigiRack Signal Generator come free with Pro Tools, as I've used it on a number of different occasions to test both my home system and a Pro Tools HD system in a professional studio. It would be fine if it just had a single tone, but it has some versatility which is definitely nice. If you need a quick signal for any reason and have Pro Tools, there's no reason to go beyond the DigiRack Signal Generator.