Select uniformly a point from the annulus $\{(x,y):1\leq x^2+y^2\leq 4\}$. Let R be the distance to $(0,0)$. Give the cdf and pdf of R.

I know that the sample space of choosing a point would be the area of the annulus ($3\pi$) and I know the method of getting the pdf from the cdf or vice versa. I’m just not sure how to start; How would I represent the distance R from the point (x,y) and would this be the cdf or pdf?