The following is a very brief explanation of Revelation 17. For a more detailed study please refer to the following link:

Revelation 12:1, 3, 16, 17: "And there appeared a great wonder in heaven (the spiritual realm); a woman (the early Apostolic church) clothed (invested) with the sun

[the Gospel light], and the moon (corroborative types of the Law Covenant) under her feet, and upon her head (intellectually guided or authorized) a crown of twelve stars (Apostles)…

(:3) "…And there appeared another wonder in heaven [the spiritual realm]; and behold a great red dragon (Civil Rome stationed in the ecclesiastical heavens starting with Constantine) having seven heads (successive and distinct forms of government) and ten horns (territorial divisions of power), and seven crowns (authority to rule) upon his heads

(:16,17)"…And the earth (stable elements of society) helped the woman (faithful church), and the earth (stable elements of society) opened her mouth (received a great amount of truth during the French Revolution), and swallowed up the flood which the dragon (civil Romanish authorities under Satan's rule) cast out of his mouth (through its infidel agencies).  And the dragon was wroth with the woman (was angry with the faithful church), and went to make war (to persecute) with the remnant of her seed (those left of the faithful church), which keep the commandments of God, and have the testimony of Jesus Christ."