In korean language, to count objects or persons or animals, you have to add a counter, there are hundreds of counters, but generally.. The counter 개 is used for objects.. And 명 is used for people.. The structure is like this :exp:공 두 개 (Two balls) ->>the object+the number +the counter..
개 and 명 are the most important. But if you forget how to use any of the other ones, the default counter is 개.
Another way to use counters besides having the counter last is this form:
두 개의 탑: two tabs
Thank you... I thought Duo was talking about a dog with two balls. That would have been weird.