It means that you believe in the restored gospel of Jesus Christ, that Joseph Smith was a prophet of God, and that Thomas Monson (the current leader of the LDS church) is a prophet of God. It means that you believe the Book of Mormon is Holy Scripture. <humor>It means that you attend many meetings on Sunday (and sometimes in the week!).</humor> Mostly it means that you should try to be the very best (most good) person you can be.