To calculate a percentage we take the number of shots made divided by the number attempted
12/15 = .8
This gives a decimal .8 we can express this in a few ways. We can say the player made 8 out of every 10 shots. or we can say the player made 80% of his/her shots. 80 percent is essentially the number of shots that would be made for every 100 shots taken 80/100 = 8/10 = .8 = 12/15 = 80%
To calculate 13% of 62 we can multiply 62 by .13 and we get
8.06