Grammar questions

I have always had trouble grammar wise when it comes to knowing when to your who and whom. I thought I would research further by using google and typing in "how do you know when to use who and whom?" I came across the site http://ask.yahoo.com/20021113.html that explained some insight to my question. AskYahoo states that "who" is used as the subject of a sentence whereas "whom" is used as an object.