Use the (epsilon-delta) definition of continuity to prove that f (x) = x^2 is continuous at every point in the interval [-10,10].

I have an exam coming up tomorrow, and i have absolutely no idea how to do this. I have watched the teacher do it time and time again, but nothing seems to help. The above is an example of something we should "know" and i dont even know where to begin. If someone could explain this as elementarily as possible I would be ridiculously thankful

please and thanks!