It's a pretty easy program. You have a timeline which you can drag the m2v file onto in one track, and two audio tracks onto for your AC3 files. Having two makes it pretty easy to set up crossfades and the like. Make a hard cut, drag the new clip from the first track down onto the second track, then extend the "borders" of the clips and create manual fades. I'm oversimplifying, of course, but a little experimentation (especially with right-clicking on everything you see) will unveil a world of options.