The charango is about the same length as a tenor ukulele in total. However, a good proportion of that is taken up by the head and the scale length is closer to that of a soprano. The neck is much wider than that of a ukulele to accommodate its ten strings arranged into five courses (i.e. five pairs of strings).
The development of the charango is very similar to that of the ukulele. The Spanish brought over their vihuelas (similar to the Portuguese machetes that preceded the ukulele) which were picked up and adapted by the locals. Rumour has it that charangos were such a big hit in Bolivia because the Spanish had banned the locals from playing their traditional music. The charangos were small enough to slip inside the poncho should any unfriendly Spaniards rear their heads.
The tuning is very similar to a ukulele. It's tuned GCEAE (the strings are in unison apart from the middle E where they are an octave apart). So you can use the familiar ukulele chord shapes to play the GCEA strings. You can just use the same fret for the top E as the other E or you can get a little more adventurous.
The scary part about the charango is that it is traditionally made from the shell of an armadillo. If you buy an armadillo charango, you'll often find hairs still sticking out from the armadillo's shell. However, the armadillo shell isn't very durable (and there are also animal welfare concerns over its use) so the higher quality charangos are made out of wood these days.
Bob Brozman is a big advocate of the charango, which he refers to as the, "South American Super Ukulele."