Question: "How can I understand the Book of Revelation?"
Answer: The key to consistent Bible interpretation, including the Book of Revelation, is to have a consistent hermeneutic. Hermeneutics is the study of the principles of interpretation. In other words, it is the way you interpret Scripture. A normal hermeneutic or normal interpretation of Scripture means that Unless the verse or passage CLEARLY indicates that the author was using figurative language, you are to understand it in its normal sense. Don't look for other meanings if the natural meaning of the sentence makes sense. Don't spiritualize Scripture by assigning meanings to words or phrases when it is very possible that the author under the guidance of the Holy Spirit means for it to be understood as it is written.
One example from the Book of Revelation that I can give you is Revelation 20. Many will assign various meanings to where it refers to a 1,000 year period. Yet, the language does not imply in anyway that the references to 1,000 years should be taken to mean anything other than a literal 1,000 year period.
A simple outline for the Book of Revelation is found in Revelation 1:19. In the first chapter, the risen and exalted Christ is speaking to John. Christ tells John to "Write therefore the things which you have seen, and the things which are, and the things which shall take place after these things." The things John had already seen are recorded in chapter 1. The "things which are" (that were present in John's day) are recorded in chapters 2-3 (the letters to the Churches). The "things which shall take place" (future things) are recorded in chapters 4-22.
Generally speaking, chapters 4 through 18 of the Book of Revelation deal with God's judgments on the people on the earth. These judgments are NOT for the church (1 Thessalonians 5:2, 9). The church has been removed from the earth in an event called the Rapture. The Rapture is described in 1 Thessalonians 4:13-18 and 1 Corinthians 15:51-52. This is a time of Jacob's trouble; trouble for Israel (Jeremiah 30:7; Daniel 9:12; 12:1). It is also a time when God is judging the world for their rebellion against Him.
Chapter 19 describes Christ's return with the Church, the Bride of Christ. He defeats the Beast, the False Prophet and casts them into the Lake of Fire. In Chapter 20, Christ has Satan bound and cast in the Abyss. Then Christ sets up His kingdom on earth that will last 1,000 years. At the end of the 1,000 years, Satan is released and he leads a rebellion against God. He is quickly put down and also cast into the Lake of Fire. Then the final judgment, the judgment for all Unbelievers, where they too are cast into the Lake of Fire.
Chapters 21 and 22 describe what is referred to as the eternal state. This is where God tells us eternity with Him will be like. The Book of Revelation is understandable! God would not have given it to us if its meaning was entirely a mystery. The key to understanding the Book of Revelation is to interpret it as literally as possible. The Book of Revelation says what it means.