Reading The Tuner
Regardless of which tuner you end up using, the basic function is the same. So I'm using this headstock tuner and you'll notice that it displays the letter name of the note that I'm closest to. In this case it's an E.
This is important to pay attention to, cause the tuner doesn't know which string you're tuning or which note you're going for, it only helps you get to whichever note you're the closest to. So make sure it displays the right note name. Later on we'll talk about what to do when this is not the case.
So now that we've confirmed it says E, notice that when I loosen the string and lower the pitch, the needle turns red and moves to the left side. If I tighten the string and raise the pitch, the needle turns red and moves to the right side. If I keep going the letter name changes, and that's where things can get really confusing, which we'll address later.
For now let's try to tune it so we get as close to center as possible. If the note is too high, meaning the needle is on the right side of the letter, most people prefer to loosen the string till it's just below the note (meaning on the left side of the letter) and then tighten the string until it's right. People say it stays in tune better that way, but I've never actually verified if it really makes a difference.
Same thing for the A string. Pick it and make sure it says A. Then adjust the tuning till it's just right. One thing that's extremely important is that you always make sure you're turning the right tuning peg. This still happens to me once in a while, where I'll do several turns on the wrong tuning peg before I realize nothing is happening. So just take the extra moment to make sure you visually locate the right tuning peg before you start to turn it.