They won the victory over him by the blood of the Lamb and by speaking the truth about Jesus to others. They didn’t love their lives so much that they were afraid to die.
Some of the angels abandoned their positions of authority and didn’t stay where they belonged. The Lord is keeping those angels in darkness, bound with chains that last forever, until judgment day.
The great dragon was thrown down to the earth, and his angels were thrown down with him. That dragon is the old serpent called the devil, or Satan, who leads the whole world astray.