Using Intellij as a model

I am working on an IDE.  I like Intellij and would like to re-use some of it's objects.  I have cloned the Intellij community code onto my local drive and got it up and running in Intellij itself.  But the project is so massive, I have no idea how to start.  For example, how would I build a Dialog Box using Intellij objects?  Thanks for any help you can give me.