This repo demonstrate the minimal viable best practice for Jenkins Shared Library.
How to use this Repo to learn?
Every subfolder in ./pipeline-scripts represents an example. Each folder comes with two file old.Jenkinsfile, representing pipeline script without shared library, and new.Jenkinsfile representing equavilent code with shared library. In ./vars each .groovy file is a Shared Library, the shared library name ./vars/${LibraryName} is the same as ./pipeline-scripts/${LibraryName}.
You can copy and paste the content of old.Jenkinsfile to Jenkins Pipeline Configuration and run once. And then do the same thing with new.Jenkinsfile.
Setup your Jenkins before playing with this Repo
Jenkins -> Manage Jenkins -> Configure System -> Search: Global Pipeline Libraries
Fill in git url, check "Load Implicitly" (if not check, you need to manually declare @Library("${LibraryName}") at begin of your Jenkinsfile). So your Jenkins system can load shared library implemented in this repo.
What is Jenkins Shared Library?
You may already very familiar with Jenkins pipeline scripts. Actually those node {}, stages("...") {}, steps { ... }, script{ ... }, withCredential() { ... } syntax are simply shared library implemented in community plugins. Those declaritive are predefined in a groovy script like node|stages|steps|script|withCredential.groovy, and you will see available parameters in plugin source code.