Today I talk about the priesthood, and the Authority of God--as stated in Article of Faith #5

We believe that a man must be called of God, by prophecy, and by the laying on of hands by those who are in authority, to preach the Gospel and administer in the ordinances thereof.

Not just anybody can baptize others in the name of Christ, nor perform the other ordinaces of the gospel.  That is something that must be given by others who have that authority.  For example, in the book of Acts in the New Testament, there is a story of a man named Simon.  He saw the apostles giving the gift of the Holy Ghost to others.  He also wanted to be able to do this--so he attempted to purchase the priesthood from Peter.  Peter taught that it the priesthood can not be bought.

We believe that the priesthood was restored in our day to the prophet Joseph Smith, and has been passed down in an un-broken chain to members of the church from that time.  John the Baptist (the same person who baptized Jesus Christ) came and restored the power to baptize to Joseph Smith, and then Peter, James, and John came and Restored the additional authority to Give the Gift of the Holy ghost--Remember that Christ himself gave that authority to those men.  You can read about John the Baptist restoring the Aaronic Priesthood here, and Peter, James, and John, restoring the Melchizedek Priesthood here.

God is a God of Order--and so He doesn't do things "willy nilly."  For that reason, even though I currently hold both the Aaronic and Melchizedek priesthoods, I can't go out, on my own, and baptize or give the Holy Ghost to anybody I want.  I must be authorized by those who are "in authority" to be able to perform those saving ordinances.  For example each local unit of the church has a bishop, who can give that authorization for me to baptize a person (after that person has been interviewed to make sure he/she is ready for baptism, and ready to take upon himself/herself the name of Christ, has repented/etc.)  That way the person who is receiving the ordinance is correctly added to the records of the church.  Along with the ordinance performed, it is recorded who performed the ordinance, the date the ordinance was performed, and what priesthood that person had who performed it.