Billboard visualization of particles - and especially their animation - is one of the more arcane concepts in Blender. We're going to shed some light on this.
Now you've got your armature, but it's not much use until you add some more bones to it. Think about your body for a moment -- you've got this thing you call a 'skeleton', which for our purposes corresponds more or less to an armature object. Read on, for more useful information!
Shape keys are modifications of the original mesh that you can animate and mix with each other. Previously called Relative Vertex Keys (RVK), one of their major uses is to create facial expressions.
A constraint is what makes everything easier, magic, automatic, customized (add more words here) in a rig. It tells a bone or an object to do something special based on the position of another object, and the position of the constrained object itself. There are many constraint types for you to play with. Most will work everywhere but, the IK solver will only be available in the Armature Editmode or Posemode.