Need help learning how to become a package contributor

Is there any websites you can recommend me?
So, I will be the do the following:

  • Write a RPM .spec file
  • Understand the RPM .spec
  • Know what commands to use to start the rpmbuild structure
  • Be able to explain to someone how the RPM .spec file works

Have you seen the docs here? They include tutorials on how to write the spec file, as well as information on the process of getting approved.

I think you mean how to build an RPM then the docs that @pg-tips posted have a link to how to use mock to do test builds. Using Mock to test package builds - Fedora Project Wiki

Collected links I have used over time.

Once your package is part of Fedora then you use the fedpkg tool.
It makes the common steps needed to maintain a package easier to get done.