Before you plug in your machine to use it you need to do a few things and learn a few things. Just like driving - you can't just jump into a car and expect to drive off without learning how to drive and making sure that there is fuel in the tank.
Luckily you don't need a sewer's permit!
It helps a lot to know how a machine works and also how to maintain one. If your machine came with an owner's manual please read it and follow the instructions for cleaning and oiling your machine. This will help you learn how it works and will make you confident about using your machine.
If you don't have the machine manual sometimes you can find your machine's manual for sale on the internet for just a few dollars. Try here if you need to do that http://www.sewingmanuals.com/
If you didn't get a manual, there is a set of 5 videos here you can watch to learn how to clean almost any machine: http://www.quilt-video.com/sewing-machine-maintenance/
If you can't watch video on your computer, and you can afford it, you can take your machine to a sewing machine repair shop for cleaning. If you can't afford that, it is still easy to figure out if you take the major cover plates off of the sewing machine (wherever you see a screw holding one on) especially in the bobbin area, and just start cleaning out dust and lint with Q-Tips and tweezers. Oil any parts that move except any belts or rubber parts. Test to see if they move by turning the flywheel toward you (counter clockwise).
Sometimes your local library will have books on sewing machine maintenance or there will be a chapter in a general sewing book that teaches machine maintenance.
**new** There is a group on Yahoo.com that is dedicated to fixing up old sewing machines! The group is called WeFixIt