Scoring is defined as marking with lines, grooves or notches. When I first started cardmaking, I found it very difficult to fold my card bases without scoring the paper first. Scoring makes it easier to fold cardstock because it breaks the fibers in the paper and makes them easier to bend.
Scoring can also be used as a subtle embellishment on a clean and simple card. Notice on this card how the scored lines frame the stamped image and provide a perfect way to center the brads. On this card I made score marks 1/4" and 1/2" from the edge of the top panel on all four sides.
There are several kinds of scoring boards and tools available, but it's not necessary to buy fancy equipment to score your paper.
Just place the paper so that the groove in the paper cutter is where you want your line, then press down with the tip of your bone folder to create the groove. If you don't have a bone folder you can use any number of other things. I have used popsicle sticks, ball point pen caps, the end of a large paper clip, and the back (dull) edge of a butter knife.
(Reminder, it's not too early to start making holiday cards! Keep in mind the Half & Half Card Challenge now through Aug 14!)
Repeated score marks (these are 1/8" apart) can be used as background embossing. Try this if you don't have an embossing tool like a Cuttlebug or Big Shot.