Ok, first. Make a generic click event. It should say "if mouse is clicked on anything, do nothing." Now go to the event that you want it to call. Create a new parameter and make it of type "object." Name it whatever you want, I'll call it "clickedObject" in my example. Now insert method into the event, from the detail panel to the events panel. Drop the method tile in the space called "do nothing" in the events panel. Alice will ask you what you want to set your parameters to. Choose something generic at first like "ground." Now go back to the method in the events panel, and change the parameter by clicking the little arrow, going to "expressions", and clicking "object under mouse cursor." Now, whenever you want to reference the clicked object in your method, just drag the clickedObject parameter tile into your method window. If you want a good example of this, see my game, escape the kitchen, and look at the click event and the method associated with it.
Just follow the link to find the game:
http://alice.org/community/showthread.php?t=3597
I hope this helps! =)