I recommend using the free app "Guitar Tuna" to tune your guitar.
You can find it on the app store, it's available for Android or iOS. You will need a google account or an Apple ID to download the app.
Once the app is downloaded and open, you will see a screen like this:
Now select each string you are tuning by pressing the onscreen button for each string.
E = 6th string (at the top of your guitar)
A = 5th string
D = 4th string
G = 3rd string
B = 2nd string
E = 1st string (at the bottom of your guitar)
When tuning the string, wind it up or down until the circle gets into the middle of the screen, and the green bars go up at the sides.
Note: Try to play the notes loud and clear while you are tuning so the app can read the notes. The notes will die away after a couple of seconds so keep playing them every 3 seconds or so while you are tuning.
Important: For new guitars, the strings go very out of tune so you will need to select each string to tune. After a while (it could take a couple of weeks depending on string type and amount of playing), your guitar will stay more or less in tune so at that point you can use the "Auto" setting. Switching auto on means you do not have to select each string, the app will listen to the string you play and guess which one it is. Watch out for very out of tune strings which will make the app guess wrong!