Can someone help me with alteration of generations?

I'm taking Biology 11 in summer school so we pretty much whizz by everything and up to a few days ago it was fairly easy, but now we've gotten to the plant unit, and it's getting really difficult. The teacher doesn't really go over everything that detailed so I have like no idea what's going on with this alteration of generations. The main reason for this is because of all this vocabulary like diplod, haploid, sporophyte, gametophyte, antheridium, archergonia, mitosis, meiosis, etc. I don't even understand these and even when I search up the definitions it does not help me at all. I was hoping that someone could explain this stuff to me in simpler vocabulary so I can somewhat grasp this concept. Thanks =/