As Jare said. Lots of info around

https://github.com/psenough/teach_yourself_demoscene_in_14_d...

https://gargaj.github.io/demos-for-dummies/#intro/1

https://demobasics.pixienop.net/

https://github.com/psykon/awesome-demoscene

http://www.sizecoding.org/wiki/Main_Page

https://www.lofibucket.com/articles/64k_intro.html