Hello dear teachers

I read in one of my books about the difference between these two words ( ability , capacity ) and the writer explained the difference in a way puzzled me a little bit so would please help me in explaining the difference in a simpler way
the writer says :
ability is a more positive quality or attainment than is capacity . a person may or may not have the capacity to learn singing : after study and practice he may or may not have the ability to sing

so please I need you help