Ditto what Dan said. If you need more info, so a search on the words "scratch stock video" without the quotation marks. The first 3 results have good info on making and using scratch stocks.
The scratch stock needs a smooth uniform surface to ride on, like the edges of the ramrod channel for example, and you need to keep the scratch stock in constant contact with that surface. Also, you need to keep the scratch stock at the same angle, in relation to the gun stock, through the whole length of the cut. Mine seems to cut better at about a 70 degree lean toward the direction of the cut. Oh, try to cut with the grain. Going against can cause chatter.
-Ron