any good source to learn about ci/cd pipelines?

Make a project. Pick a pipeline. Build that project in that pipeline. Repeat process for all the pipelines you're interested in. The sources for learning pipelines kind of suck. Just use the respective documentation for the pipeline you're working in.

There is some decent books by Dave Farley and Steve Smith but mostly about CD.
Also highly recommend Accelerate by DORA.
Id suggest starting with something like AWS CodeBuild that has a very low barrier to entry. Pick a project and build it!

Gitlab docs

@vomitmachine has the correct answer. Trial and error is the essence of software engineering.

@junon I'm glad someone else shares my sentiment. You won't get very far by waiting for answers. Gotta find them yourself.