Tablature, (also called TAB) is a way of writing down music for an instrument with strings and frets, like a guitar or a ukulele. It works a lot like the finger numbers for piano. It only shows you where to put your fingers to play each note. It does NOT tell you what the rhythm should be or how each note should sound. For that, you still need to look at the notes. Just like the piano finger numbers, the TAB is lined up with the note, but TAB is written on its own staff, underneath the piano music.
The video below shows you how TAB works on the guitar, and it is exactly the same on the ukulele.