If fx is a parabola then how would you go about graphing it?

I would draw up a simple table

-5 -4 -3 -2 -1 0 +1 +2 +3 +5 +6

Then substitute these values into the equation and that will give you pairs of coordinates which you can plot.

Of course, the numbers you choose for the top row of your table (the x values) will depend on the actual equation. This set of numbers I have showed above may not fit.

If you care to give an actual example, I can give you a better answer.