Are there any handbrake gurus out there who can help me?

I download it onto my Mac with no apparent problems, but can’t get it to open? Any immediate thoughts about something I might be missing or any advice about how to convert DVD’s to play in iTunes or on my iPod? I’m still transitioning from PC to Mac, so I’m afraid I’m not very savvy. As far as I know I’m running OSX 10.5, but not really sure how to check. The Mac is barely a year old. I just can’t figure out what I’m doing wrong. Of course, once I get it to open, I’ll have to figure out how to make it work, but I’ll be happy to just get through the first step. Much appreciation for any advice.