The Millennium is 1000 years just after the Second Coming of Christ. Those who have been saved will be in Heaven and will “judge men and angels”. The “wicked” will be in their graves and will not be resurrected until the 1000 years are over; at tht time, they and Satan will face the final judgment
The Book of Revelation follows a basically Linear Timeline from the time of the Apostles until the End of Time. There are two parallel Timelines, one showing what is happening on Earth and the other what is happening in Heaven.