Wow, you did get a good deal, especially if it's never even been used.
I'm not sure how that table works but if it has a safety strap meaning you can adjust it to only go over so far, I'd start out using that so you'll be able to get used to inverting before you go over all the way. Just be sure to relax and don't go further than you're comfortable with and gradually you can adjust it to go further when you feel more comfortable. Inverting won't do you any good if you're stressed when you're inverting, if the muscles are tense because you're scared it won't help you.
Once you get used to it you will be so relaxed when you get off of it and you'll feel all limber and stretched out. Sometimes I'll just get on and kind of float on it, it's wonderful.