Basically, some songs start with chords that are sound higher than the traditional easy ones like A, C, G, D etc. and often these chords are difficult and are used by more advanced ukulele players.
So you’ll notice some songs that recommend you to transpose it a few steps up/down. What this does is it takes that difficult looking chord and translates it into an easier one that beginners can use, by bringing it a few keys up/down.
If you want to play the song using the easier chords while still keeping its original key, you use a capo.
an example of such songs is Sweater Weather – Neighborhood. You’ll notice the chords are a bit advanced for a total beginner and will ask you to transpose it 3 half steps down, once you press the -3 on the scale the chords will be easier but the key is now lower, to stay on the same key, you put a capo on the 3rd fret and play the chords.
A C on a capoed 3rd fret is the same as an Eb but easier.
Hope this helps