Diagram of the parts of a violin and bow
The violin is the lead instrument of the string section. It is held on the left should, supported by the left side of the chin, and held from underneath by the left arm and hand at the instrument's neck. Its practical range extends from its low G string just below middle C to the high E two octaves above the fourth space E in the treble clef. During the classical era, the range only extended to the A two octaves above the A string. Beyond the seventh position the high notes are difficult to control and play in tune. The violin is played in positions that extend from first position to sixteenth (or even higher). Each position represents a hand and finger shift by the player.
The strings are tuned in fifths, G-D-A-E. Each string has particular properties that are exploited by composers and arrangers. The G string is the thickest and most sonorous of the four strings. When played in its higher positions, the sound becomes very intense and stringent because the vibrating portion of the string is constantly being shortened. The D string is possibly the least powerful of the four. It has a warm and rather subdued quality in contrast to the G string. It mellows even more when you play it in its higher positions. The A string is quite strong in first position, but loses some of its brilliance in the higher positions. This is useful for soft lyrical passages in the high register. The E string is the most brilliant of the four strings. It has tremendous carrying power when played loudly, but can be ethereal as well when played softly.
All string instruments can play double stops (two notes at once) but they are most often used on violins. With a arpeggio type of bowing, you can even play triple and quadruple stops on the violin.
Orchestras have two sections of violins, first and second, covering soprano and alto voices in most orchestrations.
There are four sizes of violin, 1/4, 1/2, 3/4, or full size. The smaller sizes are designed for young children just starting out who don't have the hand size needed to play the full sized violin.