You're talking about the Smith Machine. You probably don't want to use it alot, it can be hard on your muscles and joints because of the strict ROM. I only use it for military presses cause my god**** gym got rid of the old shoulder press station.

I typically workout alone, and just grab some random dude when I need a spotter, no one ever seems to mind. I'll usually use a different guy for incline bench than I did for decline bench, just so I'm not bugging ppl too much. If you're timid or something about this I would just find someone about to start squats or whatever, work in with them and you guys can spot each other.

And yes: always use free weights (unlees injured).