A capo is small tool you can strap around the neck of your ukulele to keep all the strings down on the same fret.  So essentially, you are barring the strings on that particular fret with a capo instead of your finger.  This is a great accessory to have in your ukulele tool box when you want to sing songs in a different key.  This capo will give you the precision needed to have keep adequate pressure on all of the strings of your ukulele.  Spring loaded capo’s are quick and easy to use and here's a pro tip, if you know the G, D, C, Em, and Am chords you can already play 1000's of songs with a capo!