Integza's channel is fun, but he repeatedly does dangerous things. Please don't use him as a learning resource.
There's a great tech ingredients series on homemade rockets and motors -- https://www.youtube.com/watch?v=OiAlUojF3Wo&list=PLzrI14lOlS...
NAR also has some good resource pages -- https://www.nar.org/
eg: https://www.youtube.com/watch?v=GzHIrAapiFg