But if you need more understanding of Rolling Hash function after watching the video, you can read this. Actually it also explains this string searching algorithm in a simple manner. If you are a beginner, I would recommend you to go through the video first, then read the material. Anyways it's a short read. Hope that would help you clearly understand Rabin-Karp algorithm.
And if you stumble into any other resources which you think is more helpful to you, please feel free to comment.