If you have a new violin that has never been played before, the bow probably does not have any rosin on it.  Rosin is usually found in a little box in the storage compartment of your violin case.
    A new bow will need plenty of rosin to get it started.  To do this, you first tighten the bow using the little turn screw at the frog end.  (The other end is called "the tip".)  Don't ever over tighten your bow!  The stick should still curve in towards the hair when it is tight.  If the stick is straight or curved upward, you've gone way too far!
    Take the rosin in one hand and the bow in the other.  Rub it up and down across the full length of the bow.  Test it on the violin strings to see when you have enough.  After this initial rosining, you will only need a little each time you practice.
    It's a good idea not to touch the bow hair or rosin with your fingers.  Sweat and oil can cause slippery areas on your bow.
     Click here for a short movie file that shows tightening the bow enough for playing, rosining, and loosening the bow again to put it away.