The violin is the hightest pitched, smallest string instrument of the violin family which also includes the viola, cello and double bass. It has 4 strings tuned in perfect 5ths.
The viola is the middle voice between the violin and the cello (refer to my "C" post). It is usually between 1 and 5 inches longer than the violin.
Music written for the viola is written in alto clef, which is rare.
Both violin and viola are made of wood and played with a bow
Here is a video of both but I would start the video about 35 seconds into it...Adele anyone?
Or a little Charlie Daniels?