(Revelation 20:1-3)
During the Old Testament satan was loose and able to inhabit people, even up to the ascension of Christ when He "preached to the spirits in prison"
1 Peter 3:19
“By which also he went and preached unto the spirits in prison;”
Which is why satan was able to possess Judas.
When Jesus went to "preach to the spirits in prison" so they could be allowed to meet Jesus because they were not offered the same option in life as we are, He then made sure satan was bound. Then began the 1000 years of satan being bound.
Revelation 20
1And I saw an angel come down from heaven, having the key of the bottomless pit and a great chain in his hand.
2And he laid hold on the dragon, that old serpent, which is the Devil, and Satan, and bound him a thousand years,
3And cast him into the bottomless pit, and shut him up, and set a seal upon him, that he should deceive the nations no more, till the thousand years should be fulfilled: and after that he must be loosed a little season.

(Revelation 20:4)
The saints who lived and died before Jesus ascension reign with Christ for the first 1000 years after His ascension, during the time which satan was bound
Revelation 20
4And I saw thrones, and they sat upon them, and judgment was given unto them: and I saw the souls of them that were beheaded for the witness of Jesus, and for the word of God, and which had not worshipped the beast, neither his image, neither had received his mark upon their foreheads, or in their hands; and they lived and reigned with Christ a thousand years.

(Revelation 20:5)
The rest of the dead did not live (wake) again until that first thousand years was over. Which began the "first resurrection" in which the dead who "live not AGAIN" until the first thousand years were FINISHED.
Revelation 20
5But the rest of the dead lived not again until the thousand years were finished. This is the first resurrection.

(Revelation 20:6)
THEN the reign with Christ for 1000 years is with those who were in the first resurrection. That reign is NOT ON EARTH as the misinterpreters suggest. It is clear to those who read this chapter carefully. 
Revelation 20
6Blessed and holy is he that hath part in the first resurrection: on such the second death hath no power, but they shall be priests of God and of Christ, and shall reign with him a thousand years.

We are currently near the end of the second thousand years. 

(Revelation 20:7-9)
This verse refers back to Revelation 20:4, saying when the (first) thousand years were over satan was let loose to deceive the nations. 
Then begins the timeline leading up to the battle of Gog and Magog, then tribulation.
Revelation 20
7And when the thousand years are expired, Satan shall be loosed out of his prison,
8And shall go out to deceive the nations which are in the four quarters of the earth, Gog and Magog, to gather them together to battle: the number of whom is as the sand of the sea.
9And they went up on the breadth of the earth, and compassed the camp of the saints about, and the beloved city: and fire came down from God out of heaven, and devoured them.

(Revelation 20:10-15)
Then satan is cast into the lake of fire where the beast and the false prophet are already (which means they are already dead before satan)
Revelation 20
10And the devil that deceived them was cast into the lake of fire and brimstone, where the beast and the false prophet are, and shall be tormented day and night for ever and ever.
11And I saw a great white throne, and him that sat on it, from whose face the earth and the heaven fled away; and there was found no place for them.
12And I saw the dead, small and great, stand before God; and the books were opened: and another book was opened, which is the book of life: and the dead were judged out of those things which were written in the books, according to their works.
13And the sea gave up the dead which were in it; and death and hell delivered up the dead which were in them: and they were judged every man according to their works.
14And death and hell were cast into the lake of fire. This is the second death.
15And whosoever was not found written in the book of life was cast into the lake of fire.

(Revelation 21:1-2)
Then the rest of the dead are judged, death and Hell are cast into the lake of fire, the old earth is destroyed and we are at the end of the timeline. THEN there is a NEW Heaven and NEW Earth.
Revelation 21
1And I saw a new heaven and a new earth: for the first heaven and the first earth were passed away; and there was no more sea.
2And I John saw the holy city, new Jerusalem, coming down from God out of heaven, prepared as a bride adorned for her husband.