how to "Make sure you have the Groovy plugin enabled"?

The docs on this page "Building and Running from the IDE":
http://www.jetbrains.org/pages/viewpage.action?pageId=983225

READ:
To  develop IntelliJ IDEA, you can use either IntelliJ IDEA Community   Edition or IntelliJ IDEA Ultimate. To build and run the code:

• Make  sure you have the Groovy plugin enabled. Parts of IntelliJ  IDEA are  written in Groovy, and you will get compilation errors if you  don't  have the plugin enabled.

What does this mean?

When i try to make the project i get:
"package org.jetbrains.groovy.compiler.rt does not exist"

so Im sure I have not completed that step.  How do i complete that step?

/usr/bin/groovy

so groovy is installed.

Thanks

-- edit --

Got it working by checking out the sources from git.  seams when you do it like that it doesnt need (or already knows) where groovy plugin is.