The pentacle is a five pointed star with a circle around it. It is usually a round disk, and flat. Upright it represents the human. It can also be in the shape of a pentagon instead of a circle. When the point is facing the bottom, it's either considered satanic, or it represents the element having more power than the spirit. The circle/pentagon around it represents the God and the Goddess.
The pentagram is a powerful symbol of protection and balance. Each of its five points represents one of the five elements comprised of the manifest elements(Fire, Air, Water and Earth) and the unifying element of Spirit. The top point represents the spirit, the left side point represents the water element, the bottom right point reps the fire element, the bottom left point reps the earth element and the right side point reps the air element. The upright pentagram represents order, with everything in its proper place. In particular, the element of Spirit is shown above the other elements - the flesh is subservient to the Spirit. The inverted pentagram is generally a symbol of evil (in much the same way that the inverted cross is), as Spirit is then ruled by the material elements. The exception to this is the use of the inverted pentagram by certain nature-based pagan religions, where such a pentagram represents the male deity, the Horned God. The Horned God is a positive force, and the two upright points of his pentagram are a stylization of his appearance.
