I'm guessing you are having trouble with getting started. The vertical bar notation on the left side of the equation means "absolute value". Absolute value is the distance a number is from 0 on the number line. I think of absolute value as a sort of mirror
that reflects negative numbers...

Usually when people use the terms input and output, they mean pretty much the same thing as independent and dependent variable. Often, an equation will have the form:
y = some function involving x
The input is a number you put in to find the output. The output is what you would...

It is still recommended by the majority of American style guides. Some people think the Oxford comma is redundant, since you are already saying "and," which is kind of the same thing as a comma in itself.
I would say a good rule of thumb is to use it, particularly when it helps...