In short
Death and Resurrection
The wages of sin is death, but God alone is immortal and will give eternal life to His redeemed. Until that day death is an unconscious state for everyone. When Christ returns the righteous will be raised and the living righteous glorified to meet Him.
Read it in the Bible
Romans 6:23; 1 Timothy 6:15, 16; Ecclesiastes 9:5, 6; John 11:11-14; 1 Corinthians 15:51-54; John 5:28, 29
This is a short summary. The church's full statements are at adventist.org, and our pastors are glad to study any belief with you.