This is a teaching concerning the end times (eschatology). It says that there is a future millennium (1,000 years) where Christ will rule and reign over the earth. At the beginning of the millennium, Satan and his angels will be bound and peace will exist on the entire earth. At the end of the 1,000 years, Satan will be released in order to raise an army against Jesus. Jesus will destroy them, and then the final judgment will take place with the new heavens and the new earth being made.