Don't get a personal trainer from your gym. The might help motivate you, but they're not really going to give you good or the best advice. If you want to learn about exercise, check out
www.exrx.net.
If your issue is motivation, then I suggest investing in a real certified trainer. Ideally, you'll want someone with a CSCS. They might be more expensive, but they're also MUCH more knowledgeable. My concern with someone who works at the gym is that they might give bad advice - I've seen people with NASM certifications who were total dimwits. You don't want them having you doing squats on the smith machine or something. Shearing forces on the knees =
Good luck!