When we "call" a function we are generally just telling the program to execute that function. So if you had a function that added two numbers such as:
return a + b
you can also call the function like this:
Which will return 8. You can put any two numbers in the parentheses in this case. You can also call a function like this:
answer = add(4,7)
Which will set the variable answer equal to 11 in this case.