The previous verse says:
(Rev 20:9) They went up over the width of the earth, and surrounded the camp of the saints, and the beloved city. Fire came down out of heaven from God and devoured them.
So all of the people that side wilth Satan are devoured, consumed, or destroyed by fire coming down from heaven. They are not being burnt forever.
Is the beast that's in the lake of fire and brimstone being burnt by fire forever? The beast is symbolic of kingdoms, nations and empires, that exist over many years, and which will be destroyed (not tormented forever, literally):
(Rev 17:8) The beast that you saw was, and is not; and is about to come up out of the abyss and to go into destruction. Those who dwell on the earth and whose names have not been written in the book of life from the foundation of the world will marvel when they see that the beast was, and is not, and shall be present.
(Rev 17:9) Here is the mind that has wisdom. The seven heads are seven mountains on which the woman sits.
(Rev 17:10) They are seven kings. Five have fallen, the one is, the other has not yet come. When he comes, he must continue a little while.
(Rev 17:11) The beast that was, and is not, is himself also an eighth, and is of the seven; and he goes to destruction.
(Rev 17:12) The ten horns that you saw are ten kings who have received no kingdom as yet, but they receive authority as kings, with the beast, for one hour.
(Rev 17:13) These have one mind, and they give their power and authority to the beast.
(Rev 17:14) These will war against the Lamb, and the Lamb will overcome them, for he is Lord of lords, and King of kings, and those who are with him are called chosen and faithful.”
(Rev 17:15) He said to me, “The waters which you saw, where the prostitute sits, are peoples, multitudes, nations, and languages.
(Rev 17:16) The ten horns which you saw, and the beast, these will hate the prostitute, will make her desolate, will strip her naked, will eat her flesh, and will burn her utterly with fire.
(Rev 17:17) For God has put in their hearts to do what he has in mind, to be of one mind, and to give their kingdom to the beast, until the words of God should be accomplished.
(Rev 17:18) The woman whom you saw is the great city, which reigns over the kings of the earth.”
As I commented in reply #105, the beast was symbolic, and so is the lake of fire and sulphur. It is symbolic of destruction. The Greek that's translated as "forever and ever" is "ice aion aion", meaning "unto the ages of ages", or until the perfect ages are due - after the 1,000 years judgement reign of Christ. Everything symbolically thrown into the fire will be tormented briefly until they are destroyed. Death and Hades are symbolically destroyed in this fire too, just as everything that goes into it is destroyed.