The violin is tuned (from low to high) G3, D4, A4, E5. The A is usually 440 hertz (420-435 hertz for Baroque tuning).
The viola is played in the same fashion, but tuned a fifth lower (C3, G3, D4, A4).
As you play, rosin from the bow will collect on the top of the fiddle. Clean this off gently with a soft cloth regularly to ensure it doesn't harm the finish or the tone quality.
There are several positions for your left hand depending how close to your face on the fingerboard your hand is. The 1st position is when your 1st finger on the A string plays B4, the 2nd position is when it plays C5, 3rd when it plays D5, etc. When a change of position is required a number is printed above or below the score to indicate which finger is used to play that particular note.
Before playing, the bow should be rubbed with rosin. You can buy some at any musical instrument store. Keep rosin in your left hand and rub the bow against it in the same way you play. Do not overdo this, since it will result in the fiddle sounding harsh.
Violins do come in several sizes, but the smaller sizes are only meant for students too small to properly play a full sized violin. If your violin is less than full size, you can measure whether or not you are ready for the next larger size by placing the violin on your shoulder just as you would play it and reaching with your fingers around the scroll. If your fingers extend all the way around the scroll and touch the pegbox (the portion just below the scroll into which the pegs fit), you are most likely ready for the next size up.
Playing with vibrato involves your left wrist and/or elbow. Keep bowing with your right hand as you normally would.