The ukulele is a four stringed instrument which looks more or less like a miniature classical guitar. Although it is today associated with Hawaii, the ukulele has its roots in Portugal, and indeed it was Portuguese immigrants who brought small ukulele-esque instruments over to Hawaii, such as the machete, the cavaquinho, the timple, and the rajão. Most of the migrant settlers came from Madeira, and so it was with this influx in the late 1800s that the seeds of the ukulele were sown, as the musical Madeirans began to play their instruments in many a street performance, spreading the popularity of the sound of their ukulele precursors.
A classical guitar will give you a good sense of how a ukulele operates, though the ukulele, as well as being much smaller, has four strings rather than the guitar’s six strings. Ukuleles also are far quieter, and like the guitar they don’t have a deep tone. Banjos have 4 strings but they can also have 5 strings, and are distinct from ukuleles in their tone which is brighter than the mellow ukulele tone.