Chords are learned with the help of a chord diagram. This will show you exactly where to place your left hand fingers in order to play a particular chord. A chord diagram is a grid of horizontal and vertical lines representing the strings and frets of the Ukulele as shown.
The dots show you where to place your left hand fingers. The number tells you which finger to place on the string just before the fret. If there is no dot on a string, you play it as an open (not fretted) string.