The following table shows the standard tuning for the Ukelele:
The G string is tuned one octave higher than expected. This is called the "re-entrant tuning".
Some performers prefer the lower G3 tuning for the 4th string. This is called the "linear tuning".
There are also some alternative tunings, which we won't cover here.
To produce different notes, press a string on one of the frets with the left hand, and pluck it with the right hand.
The following chart shows the notes produced by each string, when pressed on each fret: