help with object motion

Hi blenderheads!

I have been testing and trying to learn object motion, so I have faced few things that i would need some help.

first thing is about object rotation and keys, i learned how to make simple movement for object(rotation, move etc.).
now the actual question.
I have very low poly head, how can i make part of that object move? for example make mouth movement animation? like movement for lower lip and lower jaw?

You can use relative vertex keys for that.