D&C 11

The Lord provides instruction on two types of service in His kingdom. The being as He revealed to the Prophet Joseph Smith -

"...I say unto you, that it shall not be given to any one to go forth to preach my gospel, or to build up my church, except he be ordained by some one who has authority, and it is known to the church that he has authority and has been regularly ordained by the heads of the church." (Doctrine and Covenants Section 42:11)

This verse suggest one type is where one is given special authority or set apart where the Church knows that the person is authorized to guide, lead, and instruct groups of individuals. The second type seems to be the general obligation of all members to share the gospel and their testimony and go about doing good for he said to many early saints -

"...whosoever will thrust in his sickle and reap, the same is called of God." (Doctrine and Covenants Section 12:4)

For -

"...I say unto you, keep my commandments, and seek to bring forth and establish the cause of Zion." (Doctrine and Covenants Section 12:6)

And to all the saints -

"...no one can assist in this work except he shall be humble and full of love, having faith, hope, and charity, being temperate in all things, whatsoever shall be entrusted to his care." (Doctrine and Covenants Section 12:8)

The Lord said to Hyrum Smith which I believe applies to all -

"...this is your work, to keep my commandments, yea, with all your might, mind and strength." (Doctrine and Covenants Section 11:20)

"Seek not to declare my word, but first seek to obtain my word, and then shall your tongue be loosed; then, if you desire, you shall have my Spirit and my word, yea, the power of God unto the convincing of men." (Doctrine and Covenants Section 11:21)

"...seek the kingdom of God, and all things shall be added according to that which is just.
24 Build upon my rock, which is my gospel;
25 Deny not the spirit of revelation, nor the spirit of prophecy, for wo unto him that denieth these things;
26 Therefore, treasure up in your heart until the time which is in my wisdom that you shall go forth." (Doctrine and Covenants Section 11:23 - 26)

This type of service, required of all men, becomes clear as the Lord said -

"Behold, I speak unto all who have good desires, and have thrust in their sickle to reap.
28 Behold, I am Jesus Christ, the Son of God. I am the life and the light of the world." (Doctrine and Covenants Section 11:27 - 28)

"...I say unto you, that as many as receive me, to them will I give power to become the sons of God..." (Doctrine and Covenants Section 11:30)