Instrument Tuner by Gebauer Mattais (on Google Play store)
Piano Tuner (available on Google Play and the Apple App store)
Below is a simple demonstration for tuning a violin. In this video, an actual tuner is used. The apps above do basically the same thing. Using one of the apps above, bow or pluck a string and look at the device to see if that string is sharp (too high) or flat (too low). Try to tune using only the fine tuners! Using the pegs is quite challenging and I do not recommend it, as you can easily break a string. If you would like me to help you tune your instrument, email me at mhuang@udsd.org and we can set up a video call to go over it.
Directions for tuning a violin
Directions for tuning a viola
Directions for tuning a cello
Directions for tuning a bass