Sometimes it may be difficult to extend some areas of C4C for the first time. So this document can help you to debug the UI and find which screen and BO you should extend and also help you to identify which fields you should use.
You can get some technical information from C4C using debugMode on HTML5 version. In order to do that you should add the parameter debugMode=true in the URL.
Identifying the screen
After entering on the Debug Mode, you can hold Ctrl + Right Click on specific areas of the UI and get the Technical Information.
Note that the debug context is based on where you’ve clicked.
Note that Debug Mode does not work on IE (I use it on Chrome)
On Component Model XML you can find information about which Screen you’re seeing, Anchor you’ve clicked, Bind of some fields and more…
* Data Model also has some nice information you can explore.