The soprano also know as the standard ukulele. Soprano is the smallest out of the 4 classics. This ukulele is mostly found being carried around because of it's small size. The soprano is the ukulele for novice players who are intrestred in learning.
The concert ukulele also known as Alto is a little bigger then the soprano and instead of 13" scales like the soprano, the concert has 15" scales. This type was made for people with larger hands.
This is the type of ukulele that can be form with more than just 4 strings. It has a fuller tone then the soprano and concert type. Since the tenor type is bigger then the concert it also comes with lots of strings like 6, 8, 9, 12, and even 14.