You can find comprehensive information on AutoCAD Menus in the AutoCAD help system. Here are instructions for finding the section devoted to Menus.
1. In AutoCAD, choose Help > AutoCAD Help Topics from the menubar
2. Click on the Contents tab in the Help Topics dialog box, then double click on Customization Guide
3. Double click on Part 1 - Customization Reference
4. Double Click on Chapter 4 - Custom Menus. You will see the list of topics shown below. Click on the topic of your choice.
Overview: Custom Menus
Using Menu Files
Menu File Structure
Menu Item Syntax
Menu Groups
Button and Auxilliary Menus
Pull-Down and Cursor Menus
Toolbars
Image Tile Menus
Screen Menus
Tablet Menus
Menu-Specific Help
Accelerator Keys
You can also refer to Chapter 21 of Mastering AutoCAD for tutorials on menu customization.