What is the Priesthood in the Mormon church?

As the picture to the left shows, priesthood in the Mormon church is the power and authority of God.  However, this is a bit vague.  How does one receive the authority of God?  How is this priesthood power used?  How does the Mormon church use this priesthood?

To answer the first question, the authority of God is conferred (or given) by a man who currently has the authority of God to another man (see the picture to the right to see how this is done).  To confer or give the priesthood is often called to ordain a man to the priesthood.  This priesthood authority is often represented by keys, since keys symbolize a necessary tool to unlock a door in order to continue on to something else that would otherwise be unreachable.  Priesthood authority is necessary in order to receive certain blessings from God.  This is why the priesthood is so important.

To answer the other two questions, I'll put up a couple more posts about the priesthood in the Mormon church and how it is organized.