This video explains how to automate the 'Extract variable' refactoring using IntelliJ IDEA. Most other refactorings available work similarly. i.e. select the code to refactor → find the refactoring in the context menu or use the keyboard shortcut.
Here's another video explaining how to do some more useful refactorings in Intellij IDEA.
- Introduction to Refactoring (in IntelliJ IDEA): An article on the refactorings available in IntelliJ IDEA.