Celeste,
If it has a white selvage strip or if the edge is uncut, then fold it over to the opposite side of the fabric that looks the same. This will make a fold that lays the length of the fabric. Usually the cut ends will ravel and the selvage edges won't.
(After you cut the appropriate width strip, the selvage edge is cut off the strip as it tends to distort/pull up the edge).
I hope this helps and doesn't confuse you more.
Sis