I think a lot of the quetions here about declaring variables and or values in functions are jumping ahead of the lessons. At this point, the lesson is merely familiarizing us with the concepts of functions. In later lessons the confusion is cleared up in the use of particular arguments and how/when they are to be used.
Some people like to take small steps in learning and some like bigger steps. There is no way to cater to everyone, but all in all it is easier to learn one piece of the code at a time.