While house-keeping my old hard drive I found these videos. Although they are at the introductory level, and CLASS has since evolved quite a bit, they nontheless are a good starting point for students who want to try their hands at it. I hope they could give you a jump start as they did for me years ago. The lectures were given by Prof. Julien Lesgourgues, the author of CLASS, during the HEP Tools workshop I co-organized back in 2017 with Djuna and Graham.
This is the second of the two-lecture series:
If you enjoy the video and want to know more, you can find more courses on Julien’s website. On the theoretical side, Ma and Bertschinger is the go-to. Julien’s TASI lectures provide good intuitions on a few things in CMB and LSS, and are also highly recommended. Also helpful are TASI lectures notes by Daniel Baumann.
(Cover image credit: Brian Koberlein)