Explaining Villanelle meter for a class presentation?

[??????? ?Steph? ???????]

For my Sophmore English class, our teacher assigned groups with different types of poems. My group was assigned to present Villanelles to the class, and explain it's history, form, and meter. I took the job of explaining meter, but, Villanelles don't exactly have meters. All I know is that most 19th century poets used trimeter and tetrameter in their villanelles, and 20th century poets used pentameter.

Since it has no real meter, my teacher said to just explain what trimeter, tetrameter, and pentameter are, and an example of how poets have used them in Villanelles.

I have troubles understanding iambic pentameter, so I'm stumped on how to explain to the class how the 19th and 20th century poets used trimeter, tetrameter, and pentameter.

I'd be awesome if someone could explain these clearly, and/or tell me how to explain it to the class easily.

I've been on wikipedia, and schmoop.

Thanks in advance!~