As Jenkins plugins are Maven projects, Eclipse users have two ways to goload a Jenkins plugin project. One is to use m2e, which tries to make Eclipse understand Maven "natively", and the other is to use Maven Eclipse plugin, which makes Maven generate Eclipse project definitions. Unless At the moment, unless you have some prior experience with m2e, we currently recommend plugin developers to go with the Maven Eclipse plugin.
$ mvn -DdownloadSources=true -DdownloadJavadocs=true -DoutputDirectory=target/eclipse-classes eclipse:eclipse
Once this command completes successfully, use "Import..." (under the File menu in Eclipse) and select "General" > "Existing Projects into Workspace".
Do not select "Existing Maven Projects", which takes you to the m2e route
See Jenkins plugin development with Eclipse for gotchas and other known Eclipse/Maven related issues with Jenkins plugin development.