The Basics
On the left side of the screen is your Vocabulary, on the right is your Sandbox.
Click on words in your Vocabulary to add them to your Sandbox.
Combine words in your Sandbox to make new words!
Your Vocabulary
The words in your Vocabulary can be sorted and filtered, either by name or by tags you have defined.
Click on a word in your vocabulary to show you the word's details, which can be toggled on or off to save screen space.
Clicking on a word in your vocabulary will also add it to your sandbox on the right side of the screen. Your sandbox can have many words in it.
Your Sandbox
Click on a word in your sandbox to select it, click again to unselect it.
Once you've selected a word, click on a second word to blend them together into a new word.
New words get added to your vocabulary and you can also immediately use them in your sandbox.
Congrats! You now know how to play creative mode.