2 Nephi 32

Nephi teaches us -

"...if ye will enter in by the way, and receive the Holy Ghost, it will show unto you all things what ye should do." (Book of Mormon 2 Nephi 32:5)

Does the Holy Ghost show you or teach you all things you should do and know directly or in some other way?

Moroni testifies that -

"...by the power of the Holy Ghost ye may know the truth of all things." (Book of Mormon Moroni 10:5)

Nephi teaches us somewhat of the manner in which we learn what we should do -

"Do ye not remember that I said unto you that after ye had received the Holy Ghost ye could speak with the tongue of angels? And now, how could ye speak with the tongue of angels save it were by the Holy Ghost?
3 Angels speak by the power of the Holy Ghost; wherefore, they speak the words of Christ. Wherefore, I said unto you, feast upon the words of Christ; for behold, the words of Christ will tell you all things what ye should do." (Book of Mormon 2 Nephi 32:2 - 3)

How we know the truth of all things is what has been revealed to others by the power of the Holy Ghost wherefore we must feast upon the words of Christ. That is -

"...seek learning, even by study and also by faith." (Doctrine and Covenants Section 88:118)

Nephi chastises those -

"..because of the unbelief, and the wickedness, and the ignorance, and the stiffneckedness of men; for they will not search knowledge, nor understand great knowledge, when it is given unto them in plainness, even as plain as word can be." (Book of Mormon 2 Nephi 32:7)

The words of Christ are not just in canonized scripture but given in conference talks, handbooks, lesson manuals, and so forth, for -

"What I the Lord have spoken, I have spoken, and I excuse not myself; and though the heavens and the earth pass away, my word shall not pass away, but shall all be fulfilled, whether by mine own voice or by the voice of my servants, it is the same.: (Doctrine and Covenants Section 1:38)