How do I know which object to use for a particular method in an Anguilla project for Tridion 2011 sp1?

In the process of implementing the GUI extension, I need some commands. Example: know the current field, the current value of the field in the JavaScript file. For those found in the Anguilla documentation, we can find some methods, but what corresponding objects can be used to call these methods? How to find out about them? How to track the "focusmove" event in a JavaScript file? Please help me. Thanks in advance. An early response is appreciated.