The easiest one I know of is the Corpse Pose, where you basically lay on the floor on your back with your palms up and relax :p It would take a very long post to explain how to do each one, so here's a site that lists beginner poses and gives steps and pictures for guidance:
Stretching is the best easy exercise. Cats and dogs can stay in shape by stretching. Stretch which ever way it feels good. Best to do to slow music but can do it wherever.