Paul said he received instructions for the ordinances directly from Jesus Christ:
2 Now I praise you, brethren, that ye remember me in all things, and keep the ordinances as I delivered them to you.
23 For I have received of the Lord that which also I delivered unto you. (1 Corinthians 11:2)
Unfortunately those instructions became lost, and all that remains are its rude reflections. Thankfully, they are found in the Book of Mormon as Jesus gave them:
Who May Receive Communion?
5 And when the multitude had eaten and were filled, he said unto the disciples: Behold there shall one be ordained among you, and to him will I give power that he shall break bread and bless it and give it unto the people of my church, unto all those who shall believe and be baptized in my name. (3 Nephi 18)
Who May Not Receive Communion?
28 And now behold, this is the commandment which I give unto you, that ye shall not suffer any one knowingly to partake of my flesh and blood unworthily, when ye shall minister it; (3 Nephi 18)
Who May Administer the Communion?
1 The manner of their elders and priests administering the flesh and blood of Christ unto the church; and they administered it according to the commandments of Christ; wherefore we know the manner to be true; and the elder or priest did minister it— (Moroni 4)
How is it Administered?
2 And they did kneel down with the church, and pray to the Father in the name of Christ, saying: (Moroni 4)
3 O God, the Eternal Father, we ask thee in the name of thy Son, Jesus Christ, to bless and sanctify this bread to the souls of all those who partake of it; that they may eat in remembrance of the body of thy Son, and witness unto thee, O God, the Eternal Father, that they are willing to take upon them the name of thy Son, and always remember him, and keep his commandments which he hath given them, that they may always have his Spirit to be with them. Amen. (Moroni 4)
1 The manner of administering the wine—Behold, they took the cup, and said:
2 O God, the Eternal Father, we ask thee, in the name of thy Son, Jesus Christ, to bless and sanctify this wine to the souls of all those who drink of it, that they may do it in remembrance of the blood of thy Son, which was shed for them; that they may witness unto thee, O God, the Eternal Father, that they do always remember him, that they may have his Spirit to be with them. Amen. (Moroni 5)