There are three levels of heaven. Heaven is a dimension beyond the earthly dimension. Heaven is not limited by space or time. God resides in the third heaven. The devil and his demons reside in the second heaven. Angels can operate in the second heaven to war with the devil and his demons. Man has access to the second heaven but only those who are washed in the blood of the Lamb, Jesus, have access to the third heaven. The throne room of God the Father is in the third heaven. This is the understanding we have from the Bible.
Man is able to access good and evil from the second heaven. Therefore many religious movements can access both good and evil from this heaven. This mixture is what causes problems. In the garden of Eden, Adam and Eve operated on earth as if they were in the third heaven. In the third heaven there is absolute truth. There is no evil there and therefore no questions or opinions. Truth pervades all areas of life and there is love, peace and joy. However, because of the Fall, evil invaded the earth and now we have to contend with it on earth. Most religions embrace some of the good but they have no solution for evil. Sin produces evil actions. Jesus came to be the solution for the sin problem.
Through Jesus we can now be restored to the third heaven on earth. We can enter the throne room of God and commune with Him. Jesus sits at the right hand of the Father and we are seated in heavenly places in Him (Eph 2:6). This is the Good News of the Gospel of Jesus Christ. Read the Gospel of John where the ministry of Jesus is revealed. He came to reveal the Father and restore us who believe in Him to the Father. Now we can operate from the third heaven and overcome sin and evil from our place in heaven. What a salvation, what an inheritance.