Free online ukulele tuner
Click the microphone in the tuner, allow access, and pluck a string. It hears the note and shows you how far off you are. Green means in tune.
Standard ukulele tuning is GCEA. The G string next to your thumb is tuned high, which is part of why the ukulele sounds so bright.
How to tune your ukulele
Pluck one string at a time, somewhere quiet. The needle shows the pitch: left of centre means the string is flat, so tighten the peg. Right of centre means sharp, so loosen it. Turn slowly, small moves are enough.
New ukulele strings stretch a lot. For the first week expect to tune every few minutes of playing. That's the strings settling in, not you doing anything wrong.
How often should you tune?
Every time you pick it up. The ukulele is small and light, so temperature and handling pull it off pitch quickly. A check takes thirty seconds, and every chord you play afterwards sounds sweeter for it.
In tune? Learn your first chord
Ukulele Journey is my 42-lesson course for complete beginners, and the first chord takes one finger.