Formal:
* Reference sheet
* Summary sheet
* Fact sheet
* Handbook
* Guideline
* Manual
* Primer
* Synopsis
* Abstract
Informal:
* Crib sheet
* Notes
* Tips
* Hints
* Memory aid
* Study aid
* Cheat code
* Shortcuts
The best word to use depends on the context and the intended audience. For example, if you're creating a document for a professional audience, you might choose a more formal word like "reference sheet" or "handbook." But if you're creating a casual guide for friends, you might use a more informal word like "cheat sheet" or "crib sheet."