Small and sweet! In the purest sense, when one pictures a ukulele, the Soprano size is the most likely to come to mind. The Soprano is the smallest of the four main sizes. Smallest typically means lightest, which results in a sweet, percussive, bright tonality but with less projection and volume than it's larger counterparts.
The compact physical dimension of the instrument also translates to a shorter scale length (the length of the vibrating portion of the strings), and tighter fret spacing (the distance between each of the steel bars pressed into the fingerboard). This results in a ukulele which younger players or those with smaller hands or fingers may find more comfortable to play. The traditional tuning for the Soprano Ukulele is (high) G, C, E, A.
Despite its size the Soprano is certainly not to be considered as strictly a beginners instrument, many of the most renowned ukulele pieces recorded have been tracked using the humble soprano!