The  right hand thumb is a very powerful tool when playing ukulele and can be used for strumming, arpeggiation, and melody.  You can get a beautiful, warm tone using the flesh of the thumb or add more volume and brightness by using the fingernail.  

Many great ukulele players including Eddie Kamae, Ohta San, Benny Chong, and Jake Shimabukuro have used the thumb as a preferred choice for bringing out a variety of different sounds and techniques.  

Using the thumb is a good place to start when beginning to play both chords and melodies.  In this video lesson I demonstrate some different techniques using the thumb to play single note melodies and strumming.