The Doctrine of Christ is a very simple concept. The Lord uses these words very specifically. The Church has many teachings, tenets, principles, truths, etc., but only one Doctrine of Christ.
Perhaps the first statement of the Doctrine of Christ in modern times was given before the coming forth of the Book of Mormon:
Behold, this is my doctrine--whosoever repenteth and cometh unto me, the same is my church. Whosoever declareth more or less than this, the same is not of me, but is against me; therefore he is not of my church. -- D&C 10:67-68.
This is an amazingly broad definition of the "church" of Jesus Christ. It is important, however to understand what may included in the phrase "cometh unto me". This concept is expanded in the Book of Mormon. When Jesus first descended out of heaven to the Nephites gathered at Bountiful, He immediately clearly defined His doctrine:
Behold, verily, verily, I say unto you, I will declare unto you my doctrine.
And this is my doctrine, and it is the doctrine which the Father hath given unto me; and I bear record of the Father, and the Father beareth record of me, and the Holy Ghost beareth record of the Father and me; and I bear record that the Father commandeth all men, everywhere, to repent and believe in me.
And whoso believeth in me, and is baptized, the same shall be saved; and they are they who shall inherit the kingdom of God.
And whoso believeth not in me, and is not baptized, shall be damned.
Verily, verily, I say unto you, that this is my doctrine, and I bear record of it from the Father; and whoso believeth in me believeth in the Father also; and unto him will the Father bear record of me, for he will visit him with fire and with the Holy Ghost.
And thus will the Father bear record of me, and the Holy Ghost will bear record unto him of the Father and me; for the Father, and I, and the Holy Ghost are one.
And again I say unto you, ye must repent, and become as a little child, and be baptized in my name, or ye can in nowise receive these things.
And again I say unto you, ye must repent, and be baptized in my name, and become as a little child, or ye can in nowise inherit the kingdom of God.
Verily, verily, I say unto you, that this is my doctrine, and whoso buildeth upon this buildeth upon my rock, and the gates of hell shall not prevail against them.
And whoso shall declare more or less than this, and establish it for my doctrine, the same cometh of evil, and is not built upon my rock; but he buildeth upon a sandy foundation, and the gates of hell stand open to receive such when the floods come and the winds beat upon them. -- 3 Nephi 11:31-40.
This appears to be an expansion of just what it means to "come unto Christ": it includes repenting, being baptized, and becoming as a little child.
It should be noted there is one extremely important part of the Doctrine of Christ which is nearly always overlooked. As Jesus told His disciples, if they do not become as little children, they cannot inherit the Kingdom of Heaven (Mat. 18:3)! The way Jesus repeated the requirements in a different order, it is clear that one may become as a little child either before or after baptism, but both steps are essential in order to enter the Kingdom of God!