*how do you do input and output with equations,*

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 be calculating. A really simple example: you want to know how much money you'd have to spend total if you are getting some number of $10 t-shirts.

The number of t-shirts is the input, or independent variable, which we will call x. The total amount of money you are spending is then the output, or dependent variable (because it
*depends *on the number of t-shirts), and we will call this y. The equation you would need to solve this problem for any number of t-shirts is:

y = 10x

You would put in (*input*) the number of t-shirts you are getting in place of x, and would come out with the total amount of money you'd need to spend (*output*).

Hope that helped :)