20 years old isn't very old. I have my mom's old one, which is 35 years old, because she prefers Grandma's 1942 Singer. The newer your sewing machine, the more complicated it is to fix stuff like broken needles!
Seriously, I suggest you call a service center and make an appointment to have it serviced, and tell the person there that you don't know anything about it, and ask them to SHOW you how to do this kind of basic stuff as part of the servicing, rather than just dropping it off to have it done.
That's what I did.
Those guys were totally sweet about it--showed me all kinds of stuff I would NEVER have known was important about the tension knob and how different threads affect the tension, why different fabrics need different needles, why you need different foots, bobbins and bobbin case stuff, where your machine needs to be oiled, how often it needs to be oiled, what oiling it does--they even showed me how to work the decoration cams that came with it that I'd never seen used before. I had no idea that lint could build up inside some of those places and that I needed to canned air the sewing machine!
It's the best $50 dollars I ever spent in furtherance of my in-fits-and-starts crafting schemes.
I have the manual that came with this one--it's in a plastic packet inside the case, but it's always been of limited use to me. Taking it to the service center for some hands on instruction was much more useful.
