How can I help my friends understand why Mormons don’t believe in the rapture? What should I do to help them understand?
Mormons don’t believe in the rapture, because we do believe in modern and continuing revelations through Prophets. Doctrine and Covenants sections 63 and 88 give us a better understanding of what will happen at the Second Coming of Christ.
This might be enough to help them understand, but chances are they will need to gain a testimony of the truthfulness of the Book of Mormon and of Joseph Smith‘s calling as a prophet, before they would be willing to accept anything found in the Doctrine and Covenants.