Take a look at the another current topic, "Singer Touch and Sew" here in Vintage Machines. If you don't have a manual, you'll probably need to get one from the Singer website. Go here -
http://www.singerco.com/support/instruction-manuals and type in 648. You should see two results - one is buy a manual, the other is a free PDF download.
If all else fails, find yourself a Joann's 40% off coupon and buy a Sidewinder.
Tate