The answer
The concept of salvation, the intercessions of the saints, Saint Mary as the Theotokos (Mother of God), and the Holy Sacraments are all vital differences between the Orthodox Church and most of the Protestant Churches.This link is very resourceful for learning more about the Orthodox Church and will help you to understand the differences.
http://www.suscopts.org/resources/literature/orthodox-faith/
These books by H.H. Pope Shenouda III of Blessed Memory compare and contrast the differences between the Orthodox faith and the Protestant beliefs:
Comparative Theology
Salvation in the Orthodox Concept
Answered by His Eminence Metropolitan Youssef (opens in a new tab)