I know how derivatives work and how to find them can you

Question

Let f(x) = x² - 2x +1

First part required to find the derivative which I found to be f '(x) = 2x - 2

I don't understand how to find the slope of tangent at x = 4 or how to find the equation of the tangent line using y = mx + b

I know how derivatives work and how to find them. Can you explain to me using the information how to find slope and equation?