In short
The Great Controversy
All humanity is part of a great struggle between Christ and Satan about God's character, His law and His rule. The conflict began in heaven, came to earth and will end when Christ wins. In it God is always on the side of love and freedom.
Read it in the Bible
Revelation 12:4-9; Isaiah 14:12-14; Genesis 3; Job 1:6-12; Romans 1:19-32
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.