Strings

Violin is probably the most popular string instrument.
It's the highest in tone, with G, D, A, and high E strings.
Violinists use treble clef to read their music.

Viola is not as popular of a string instrument as the violin.
They are slightly bigger and lower than the violin but higher than the cello and have the C, G, D, A strings.
Violas also rarely get the solo parts and usually play the background.
Violists use the alto clef to read music.

Cellos are the second lowest string instrument and are probably the second most popular.
They have the same strings as the viola (C, G, D, and A). Cellists read bass clef.

Double bass is the lowest string instrument and has the E, A, D, and G strings.
They are also used mainly for background music. Double bass players also read bass clef.