The hard thing about learning how to parallel park is trying to get the car close enough to the curb without hitting it. A curb is the edge of the sidewalk beside the road.
When you're using the word curb as a noun, it's the raised edging beside a street. When curb is a verb, it means to restrain or hold back, like when you curb your impulse to laugh while watching a badly acted play. Curb comes from the Latin word for "curve," curvus, which describes the shape of a restraining strap on a horse's head — in the fifteenth century, this band was called a curb.