From A Wiki of Ice and Fire
The horn is 6 feet (1,83 meters) long. It is made from the horn of what must have been an enormous dragon. It has a black gleam, and is banded with red gold and Valyrian steel. When touched the horn feels warm and smooth. Its surface is shiny and reflective, though the reflection depicted is somehow twisted. The bands of the horn are covered by strange writings, Valyrian glyphs. When the horn sounds, the glyphs glow red-hot and then white-hot.
A Feast for Crows
Dragonbinder is brought to the kingsmoot by Euron Greyjoy when the ironborn elect a new king. Euron claims to have found amongst the smoking ruins that were Valyria. The horn's noise silences all and ends the possible fight between the supporters of Victarion and Asha Greyjoy.
The horn's noise sounds like the screaming of a thousand souls and it seems to listeners as if their very bones are aflame and searing their flesh from within. Cragorn, the man who blows the horn for Euron, collapses with blisters on his lips, and the tattoo he has of a bird on his chest is bleeding.
Euron wins the kingsmoot by promising the ironmen that they will conquer Westeros with dragons. When Asha argues that there are no more dragons, Euron tells her that there are three, and he knows where to find them. He does not mention that the dragons belong to Daenerys Targaryen.
A Dance with Dragons
Euron gives Victarion the horn when he sends him to Meereen to bring Daenerys Targaryen back to him. He has it with him aboard the Iron Victory. According to Moqorro the Valyrian glyphs on the horn read:
|“||I am Dragonbinder ... No mortal man should sound me and live ... Blood for fire, fire for blood.||”|
Moqorro says whoever blows the horn will die but any dragons that hear will obey the horn's master. Moqorro says Victarion must be made the horn's master and he must claim the horn with blood.
The Winds of Winter
When Victarion and the Iron Fleet arrive at Slaver's Bay, Victarion still has the horn with him in his cabin. Some of the Iron Fleet arrives at the bay of Meereen just as the Second Siege of Meereen is about to begin.
|“||Bight and baneful was its voice, a shivering hot scream that made a man's bones seem to thrum within him ... It is the horn of hell.||”|
|“||That horn you heard I found amongst the smoking ruins that were Valyria, where no man has dared to walk but me. You heard its call, and felt its power. It is a dragon horn, bound with bands of red gold and Valyrian steel graven with enchantments. The dragonlords of old sounded such horns, before the Doom devoured them. With this horn, ironmen, I can bind dragons to my will.||”|