A pot is used for boiling water, or cooking stews and soups. They typically have two small handles on each side.

A pan has short, usually curved sides, and is suitable for simmering small amounts of liquid, searing or frying. It will almost always have a single long handle.

Woks are the exception- the look halfway in-between a pot and a pan, though the design is more geared towards the same uses you would use a pan for. Although there are two small handled varieties, the thinness of the metal makes it much less effective at stews and soups because it doesn't hold heat well.