Are you talking about the sampler? With the sampler you can use it like most other samplers (I'd recommend the more advanced sampler in there, I think it's called the NNXT). I have a shitload of sampling techniques I use. Taking a sound I like (cd, vinyl, tv, etc) and throwing it in the sampler. From there, I can try a few things. If it's a general tone, I might loop and crossfade the end to sustain it. If it's a melody and I don't want to change my bpm, sometimes I'll make it fit on only one key (after I find the key I'd like it in), then I change the start time to play the first note of the melody. Then I'll copy the zone and paste, move it to the next key (so it'll play on ONLY that key) and change the start time to the next note. On and on until Have the whole melody, so I can play it to the beat. Those are a few tips for creating your own banks in the sampler. Those tips can work for pretty much any decent sampler as well, not just reason's.
With the subtractor, I mainly just use it for making a bass tone, or layering it under another bass line, drum, whatever.
If you're looking for sound banks, you can load soundfonts into the sampler as well. If you search on the net, you can find a grip of soundfonts.