All the events for the selected item in the left dropdown will be listed in the right dropdown.
If you see an item of interest, let go of the mouse button and the VBA editor will insert that event's procedure declaration in the code module.
For help on a particular object or event, select it in the Object Browser and press F1 for Help on that topic (note that not all events are documented -- you may have to access event information by going through the object to which the event belongs.
Another method to determine what events are available is to create an empty class module, and enter the following code: elements in the left side dropdown at the top of the code window.
Since VBA can cause an event procedure to run, it is possible that your code may end up in a loop.
Event procedures must be declared exactly as they are defined.
An procedure that is executed automatically by Excel when the event is raised.
It is important to remember that in addition to user input, events may run as the results of actions taken by other VBA code.
For information about supressing events for controls on a form, see Suppressing Events In User Forms.
Events on Charts are a special case of events and need special code handling.