Here's a reasonably clear reference, or at least one with a picture:
http://www.stewmac.com/cgi-bin/hazel.cgi?action=SERVE&sku=I-4000&PG=3&s1=Free_info_sheets&item=freeinfo/fi.html
A more common name for the "sweeper" would be the wiper.
When one uses a potentiometer it is usually to get a fraction of some signal coming out of the wiper, the fraction depending on the location of the wiper which is attached to the shaft. The commonest configuration would feed a signal to the clockwise-rotation end of the resistive strip, tie the other strip contact to signal common or "ground", and take the wiper contact (usually the center of the row of three) as the output.
If you have the shaft fully clockwise you should have the wiper directly connected to the signal. If fully counterclockwise, you should have the wiper tied to signal common. Anywhere else you will get some fraction of the input signal.
With the pot shaft facing you and the contacts pointed down, the ccw contact is usually on the left, cw on the right.
EDIT: actually that link is not very good---the picture is about the only thing to recommend it. But I haven't been able to find a better one as yet.
