You can access the tuner under Options in the song pause menu. You can also access it from the main game play screen.
When you access the tuner, the Auto mode is toggled green. This means that when you pluck a string on your guitar, the tuner suggests which string you are tuning.
Tuning in manual mode is useful if the strings are too out of tune, or if you are tuning new strings for the first time.
Tuning in auto mode
Start tuning your guitar by plucking the top string. It is the first string you see as you look down on your guitar; the string is also known as the low E string. When you pluck the string, the tuner shows if you need to tune the string up or down.
If the tuner shows that you need to tune down, turn the tuning peg for the E string towards you. If the tuner shows that you need to tune up, turn the tuning peg for the E string away from you.
The string is in tune when it's in the middle on the tuner window. Repeat with each string; that's it, your guitar is in tune.
Tuning in manual mode
To start manual tuning, select the E string peg on the tuner screen. When you do this, you hear what the tuned string should sound like.
Pluck the E string and the tuner shows if you need to tune the string up or down. If the tuner shows that you need to tune down, turn the tuning peg for the E string towards you. If the tuner shows that you need to tune up, turn the tuning peg for the E string away from you.
The string is in tune when it's in the middle on the tuner window. Repeat with each string; that's it, your guitar is in tune.
Check the following video for a more in-depth tutorial about tuning your guitar.
If Yousician can't hear you at all, check troubleshooting tips here.
Next up: Choosing your set up for guitar