If you mean, what is Sonar... Sonar is audio and MIDI recording software. It runs on PCs.
If you've got any experience with the old Cakewalk Pro Audio software, this is pretty much that with a few pieces of chrome added to the fuselage. For example if y ou've got a sound module (let's say a synth) you can record your MIDI into Sonar (via your sound card) and then, without having to open a second program, use that recorded MIDI to trigger your synth and record the audio without having to have a second program or even open another window. Of course you can also just record your bass into your sound card.
Talking of which you'll want a fairly decent sound card to get your stuff into and out of the computer. In other words a Sound Blaster may or may not cut it-- you'd have to be the judge of that.
I'm not aware of any recent versions of Pr* T**ls running on Wintel. Oh, and certain versions of Pr* T**ls require you to use D*g*d*s*gn's own hardware in order for it to be usable. So the up-front cost might be a little more than you bargained for... which is part of the reason a lot of people (myself included) hold it in some degree of disdain. I'd stick with Sonar myself.