If you try to play with a brand new bow with brand new horse hair on a brand new string nothing will happen. No sound whatsoever. Often a luthier will when the hair has been properly a fixed to the bow use prepowdered rosin and work it in thoroughly coating every hair, as besides supplying traction where it meets the string it also acts as weather proofing and preservative, it was part of the mummification process used by the Egyptians. For a normal getting ready to play rosining hold the bow by the wood in one place and move the rosin back and forth. As you do try to keep moving the rosin so as not to wear a groove in it especially when using an expensive rosin. A cheap ($3.00 or under) or broken piece of rosin may leave you with no option but to notch in which case notch away, you try to be as careful as you can but you will probably will drop and break your rosin long before you'll wear it out. Take a small piece between two fingers and crush it. It will fine powder instantly, pretty neat trick, use this rosin on any skipping spots on your horse hair from getting grease or wax on it. Occasionally rosin the back side of the horse hair for the reasons given above. Try not to touch your horse hair with your fingers any more than necessary and before you do wash your hands with dish washing soap to be as degreased as possible. If someone does touch your horse hair with their fingers try not to throw a fit. I like to encourage people to touch the extra hair where it sticks out to their hearts content while I tell them about horse hair and rosin. If you were to look at horse hair up close you would see sort of herring bone structure, this is what grabs the rosin and holds on to it but only in one direction, and like any natural hair its thicker at one end and gets thinner as it goes along. If you were to take the horse hair right off the horse and put it on a bow as you rosined it you would feel it grab one way and slip easier the other way, and the rosin wouldn't last as long that direction. One of the knots would look smaller then the one on the other end. For these reasons the horse hair must be divided in half, one half turned around and put back against the other, a different direction selected, pulled apart, turned around etc. over and over again making sure enough is traveling both directions before even beginning to prepare it for a specific bow. The highest quality synthetic horse hair has some form of ridging both directions but none hold rosin as well as real horse hair. Violinists prefer white horse hair for a variety of reasons but black horse horse is thicker, sturdier, and grabs the rosin and the string harder and is preferred by Cellos, Basses, and Viols. Be sure to check out "Rosin" on Wikipedia to see its many uses. I hope this is helpful, Keep on Psalting!