Here is a picture of the fretboard of the ukulele.
You can print this off and then cut it out and use it to practice putting your fingers on the proper strings to make the chords we have learned!
You could also draw on some colored dots for each chord. Here are some charts below for the different chords. You can color code the dots if you wish by printing it out and coloring them in.
A really good free app to help remember where to put your fingers is called: Real Ukulele and The Ukulele App (by Jon Howard)