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
Revelation 20 the Millennium begins when Satan is chained in the Bottomless Pit and the Righteous Dead are raised in the First Resurrection. At the end of the Millennium the Rest of the Dead are raised (Gog and Magog)and will face the Great White Throne judgment and the Lake of Fire (Hell).