Your saves for all games on your PC. All that Steam cloud does is create a backup of those saves. So, if you lose your hard drive or something you can download them back to your PC from the cloud. Having said that, there have been reports where Steam cloud has bugged out and it kills all your saves. Personally I turn it off for saves I care about like SR2 and SRTT.
You can find your local SRTT saves here:
..\steam\userdata\[some #s]\55230\remote\
The numbers above are your unique Steam ID btw.
You don't need to know any of that for the save editor though. It should always automatically open your folder to load them right there by default.