You either get a violin teacher to teach you how to tune it properly or you go to a music shop and ask for help.
There is a lot you need to know.
1) 1st you need a beginner's book that will teach you the names of the parts of the instrument.
2) You use the wooden pegs to get the strings almost in tune, but you also get the fine tuners , loose first, so that after you tune with the pegs, the fine tuners can be used to get more closely in tune.
3) You need to know how to check the bridge and make sure it is straight. If it leans any, eventually it will become warped. Sometimes the strings have to be loosened some to allow you to straighten the bridge and then retightened and retuned.
4) When the strings are new, on some violins they may slip out of tune easy and frequently. But in a few days they are more stable. After that the violin should stay pretty much in tune, except if it gets bumped, or sometimes a change of weather will make it go out of tune.
Cold weather, or rainy, or humid weather are factors in the violin slipping out of tune
5) Even if you cannot afford a teacher on a regular basis, you at least need one long enough to get you started and to teach you care of instrument, basics,and tuning of the instrument.
6) also the names of the strings which are G-D-A-E. The fattest string is the G string. This is the same G that is the one below middle c on the piano. But a violin pitch pipe or an electronic tuner makes it easier to tune. The next string is D which is the same as the D right next ot middle C, but like I said the pitch pipe made for a violin is better. The next string is the A- (440) . This A is located to the Right of middle C. And the last string is the E, which is about 10 notes above middle C. The E string is the thinnest string, and it is the highest pitch string.
1st it is best to tune the A string. Next you tune the D string, Next you tune the G string. Then check to make sure the A is still in tune , Then tune the high E string. Some cheaper violins , fall out of tune by the time the G string is tuned and it may take more than one try to get it all in tune. Don't let that discourage you. You will eventually get it. If you tune the strings to the piano , they won't be exactly in tune. That is why the electronic tuner is better. Also, the pitch pipe sometimes doesnt' blow a nice clear sound. The Tuning Fork is always in tune, but it is just for the A- string.
Once you learn to tune the 440 A, Then if you can learn to hear fifths, YOu can bow the A and D together to tune the D , then do that with the D and G, then do that with the A and E strings. Tuning by playing 2 strings together, you can learn to tune by 5ths and get a much better in tune.
Hope this helps.