Tuning your violin can be a tricky task.
When you first purchasa a violin, hopefully, it will already be set up and tuned properly. But the violin is sensitive to everything, so strings can easily slip out of tune. If it is brand new, it can take a little while for the strings to settle down.
The violin strings are pitched from concert A so this is the first string to tune. After that the strings are tuned in perfect 5ths, and a skilled musician can tune by listening to the sound of 2 strings played together, and making that perfect 5th between each pair of strings. You may have seen orchestral violinists tuning by playing the strings in pairs, and simultaneously moving the pegs to tune. This is a complex skill, and can take years to achieve.
If however you don't know where to start, you can download a tuning app on your phone or tablet, which will helpfully sound the note you want, and you tune to the sound it makes.
Start by sitting comfortably and holding the violin on your lap with the strings and pegs facing towards you.
The lowest string on the violin is G, followed by D, then A and the highest string is E.
By turning the pegs away from you, you can make the note higher. By turning the peg towards you, you can make the note lower. BE CAREFUL not to turn too much - if the string is too tight it will break. As you turn the peg, you need to push the peg in, to keep it in place. Don't push too hard, as it will become even more difficult to turn.
The pegs help you to get the tuning nearly right. Then you use each of the fine tuners, located below the bridge, to get it exactly right. Turn to the right to make the note higher, turn to the left to make it lower.
I recommend the App, Master Violin Tuner, to get you started.