I really don't understand this topic at all. I'm so confused and have no idea how to even begin this problem.

a) Use the epsilon-delta definition of limits to show that f(x)= x^{2}is continuous on all ℝ.

b) Now do the same for g(x)= x^{2}for x≥0 and 2x for x<0.

I've tried to figure this out, but I can't wrap my head around this no matter how many examples I look at.