Pentacles

One reason for confusion is that pentacles are used in many different ways by different religions. Pentacles are often confused with pentagrams, which are five-pointed stars. Pentacles are simply pentagrams inscribed in a circle. Most religions use it with a single point facing up. In this orientation, it represents many things: power, protection, life, and health. It is also used as a symbol of a witch's belief, like the Christian cross, or Jewish Star of David.
When the single point is facing downward, it signifies something different. An inverted pentacle is sometimes used to represent negative energy. There are, however, uses of inverted pentacles that aren't negative. They're used in initiations to show that the initiate is looking within themselves, altering their bad habits and perspective to become a better person. Inverted pentacles are also sometimes used by witches to represent the Horned God.

Questions of right-side up or upside-down aside, there still remains a lot of meaning in a pentacle. Each point represents one of the five elements: earth, air, fire, water, and Spirit. The surrounding circle represents eternity and the binding of the elements together.
The placement of the elements on the star varies, with different meanings for each arrangement. The one constant in all upright pentacles is that the top point is always Spirit, showing that Spirit is above the other elements.
One arrangement has fire at the upper left point, earth at the lower left, water at the lower right, and air at the upper right. In this version, earth and water are on the bottom because they are the grounding elements. Fire and air are higher because they are the action elements.
Another arrangement follows a creation story. Start at the top with Spirit, which represents the deity. Go down to fire, at the lower left point. Fire represents the will of the deity to create everything. The next stop is air, in the upper right point. Air represents the words of creation. Across to the upper left point and water, which represents life. Down to the lower right point, where the element of earth represents the earth forming from all the other elements. Finally, going back up to Spirit represents the earth trying to return to the Spirit.

Pentacles are used many ways in pagan rituals and ceremonies. One way they're used is as invoking and banishing pentacles. Traced in the air, or drawn just about anywhere, they are used to invoke positive energies into the circle, or for protection and banishing negative energies.
Concrete forms of pentacles are used in ritual, too. A working pentacle, made from wood or paper, is black on one side and white on the other. It is used to give magickal energies form and shape. A ritual pentacle is a circular dish with a pentagram inscribed on it. It's connected to the element of earth, and is made of clay, wood, stone, or metal. It's used to hold cakes and wine for blessing, and requests or petitions for spells.
Pentacles also show up in tarot decks. Used as a card suit, pentacle cards represent earth, abundance, and money.

Though pentacles are largely seen as a pagan symbol, many other cultures use it. Pentacles show up on relics from Babylon, Egypt, Celtic lands, and even the early Christians. There are, in fact, quite a few Christian meanings of the pentacle.
Pentacles are used to symbolize the five wounds of Christ: the crown of thorns, and the nail wounds in each wrist and ankle. They also symbolize Man with arms outstretched. An upright pentacle symbolizes the power of God over the elements. Similarly, an inverted pentacle represents evil by showing the world of matter, or Satan above God.