It's a daunting task. [Insert sigh of frustration here.] At this chilly time of year, especially with our constantly changing weather in the DC area, violins and violas have a tough time staying in tune. For the inexperienced player or parent of a string player, you run the risk of breaking a string when you tune the instrument. This site provides tuning pitches for each of your strings. If you can use your fine tuners to get the strings in tune, use them. If the string is so far out of tune that you must use the pegs to tighten them, proceed with caution. Starting with the A string, pluck or bow to hear its pitch and compare it to the tuning pitch on this website. Chances are, you will need to tighten the peg. The strings are wrapped snugly around each peg so they don't typically tighten on their own -- they're more likely to slip out of tune. Gently turn the peg - gently! While you do so, push the peg into the peg hole a little bit to help it stay in place. Listen to the tuning pitch, pluck the string, and turn the peg again if necessary.
I could write pages on the tuning process, and this is just a start. If you're unsure of how to tune, ask your teacher. It takes years of practice to become proficient at tuning your instrument, so be patient!