Basically, you load in a video. Encode it to AVI first, just to do this with, so it doesn't have to look good. You just need it for time referencing. I had trouble working from MPEG2. Basically, you type in the caption you want, and hold down APPLY as the section of video you want the subtitle on plays. It'll write the timecode and you can export it to whatever format you need to import into DVD-lab (I did).
I just looked at the program, though, for the first time since I did that project and it's a bit more tedious than I remember. Still, though, it did produce results.