Question

What is a bin width and 7 bins for a histogram?

Answer 1

if you have some numbers, you can sort them, and then put values "close" together into the same "bin". A histogram will plot the number of values in each bin.

But you have a choice of what values go into a bin.
for example, putting all values between 0 and 1 into the first bin
compared to putting all values between 0 and 10 into the first bin
the bin width in the first case is 1, and in the 2nd case, 10

Answer 2

If they want you to use 7 bins,
then I would take the biggest number - the smallest number
in your list
then divide that range by 7 to get the "bin width"