Jeez, you ask this stuff when I'm not awake yet....
Viola is strung A, D, G, C. (high to low) This makes it a 5th lower than a violin. Sheet music is in Alto clef. Also called C clef. (Treble clef is G clef)

If you just play the same fingerings as a violin, you are a 5th lower. ie, Key of G turns into Key of F, etc. The back up players will love this. Not.

If you don't 'stretch' your fingering hand, your intonation will be flat but it's not that difficult to do. My hands are small and I can play a viola.

Slow airs, laments, etc are magnificent on a viola. Start with those.