it has four strings, usual made of nylon like classical guitars. g-c-e-a is the standard tuning. a guitar is e-a-d-g-b-e. a good way to look at it is that the guitar is tuned to fourths. so is the uke, but in a different key. g to c is a fourth, c to e is a third, just like the g to b on guitar, and then another fourth from e to a. start by experimenting with similar cord forms as guitar, and adjust as you see fit. if you know how cords are constructed, you could just break it down note by note. for instance, a c major triad would be the 1-3-5 of the major scale, or c-e-g, played at the same time, so just look for those notes on the uke fretboard. these three notes are already there in the standard tuning, plus it has the sixth, a, the relative minor. you could explore alternate tunings so much on a uke.
pretty much, once you see scales as whole, or two fret, and half, or one fret, step patterns, you can play just about any instrument to some degree. just learn the key signatures and try to think of the guitar or any stringed instrument as sections of a keyboard cut up and stacked ontop of each other at certain intervals. eventually, you can look at the fretboard and have a mental map of different keys. hope this helped some. good luck.