How much about the implementation of randomized SVD implementation in Notebook 2 should have been understood when Rachael moves on to Notebook 3?

I watched till 0:24:42 in Video 4 when Rachael moves from Notebook 2 to Notebook 3. I am still a little bit unsure about randomized SVD implementation. I am not sure what LU decomposition is. Is that implementation function like a Maths formula that we are supposed to look up/remember instead of understanding why that works? This is for the purposes of this class.