According to Daniel, this story means there will be ten leaders who come from one group, and then another different leader will appear and take over three of them. This shows a time when leaders change, and someone new and powerful comes along.
Daniel 7:24: And the ten horns out of this kingdom [are] ten kings [that] shall arise: and another shall rise after them; and he shall be diverse from the first, and he shall subdue three kings.
Revelation 17:12 describes ten kings receiving power at the same time, whereas Daniel 7:24 describes ten kings arising one after another.
Revelation 17:12: And the ten horns which thou sawest are ten kings, which have received no kingdom as yet; but receive power as kings one hour with the beast.