I'm a beginner, too, but I look at it this way: (+) is the uncurried, unsectioned add function. You use (+) when it happens to be convenient or necessary to use it the way you'd use functions that you give names, e.g. passing it to another function the way you do with map.
A section, on the other hand, is a partial application of a function, and the way to remember what happens to the input it takes is to notice which operand is inside the parentheses of the section.
( / 8) is the function that, given n, returns n / 8.