The default interaction model with Jenkins, historically, has been very web UI driven, requiring users to manually create jobs, then manually fill in the details through a web browser. This requires additional effort to create and manage jobs to test and build multiple projects, it also keeps the configuration of a job to build/test/deploy separate from the actual code being built/tested/deployed. This prevents users from applying their existing CI/CD best practices to the job configurations themselves.

With the introduction of the Pipeline Plugin, users now can implement a project's entire build/test/deploy pipeline in a Jenkinsfile and store that alongside their code, treating their pipeline as another piece of code checked into source control.

Getting Started

• The Pipeline Plugin has this, fairly comprehensive, tutorial checked into its source tree.
• Overview of Continuous Delivery with Workflow
• DZone Refcard
• Pipeline as code "cook book"

Additional Resources

• Pipeline Plugin page 
• Plugins compatible with Pipeline
• Stack Overflow "jenkins-workflow" tag
• Examples repository

Presentations

Presentations given by Unknown User (jglick), author of the Pipeline Plugin:

• 2014 presentation (with slides)
• 2015 presentation

Other presentations:

• Pimp your Continuous Delivery Pipeline with Jenkins workflow (W-JAX 14) by Cyrille Le Clerc

Blog Posts

• Getting started with Jenkins Workflow by Udaypal Aarkoti
• Multibranch Workflows in Jenkins by Kishore Bhatia