The cavaquinho is a scion of the ukulele family. It developed from the same Portuguese instrument as the uke: the machete. The machete developed into the Cavaquinho in Brazil. Hence, today there are two distinct types of cavaquiho: the Portuguese cavaquinho and the Brazilian cavaquinho.
Like the uke, the cavaquinho has four strings but these are usually tuned D, G, B, D (creating an open G chord). This gives the strings the same relative pitch as the slack-key ukulele tuning. The strings go from low to high rather than being re-entrant and are usually steel strings.
If you're used to uke chords, you can tune the higher D string up to E. Then all the ukulele chord shapes you know will work on the ukulele.
DAddario J93 4 String Cavaquinho Set