"The star is small."
Translation:Der Stern ist klein.
Kurz means short; it's not used for people though, in the sense of "a short person".
However, kurz doesn't mean small. To mean 'small' in German, as in this sentence, you need to use the word 'klein'.
Additionally, 'klein' can be used about humans to mean "short". So it could be said that 'klein' is used both with people and with objects, while 'kurz' is only used with objects.