Where Are the Stepstones?
The Stepstones are a group of small islands located east of Westeros (further east than Dorne) and west of Essos, between the Narrow Sea and the Summer Sea. Their location has historically made them a key area to control for trade, but by the same token, has made them a prime location for pirates, criminals, and others. Like other locations in the region, their rule is largely disputed.
The Stepstones' Significance in "House of the Dragon"
At one point — right around the time of "House of the Dragon" — an alliance of Free Cities, known as the Triarchy, works together to rid the Stepstones of pirates and make it a safe passageway. However, the nobles of Westeros soon grow frustrated by the ambition of those holding the islands (not to mention the high tolls they exact on ships passing through), and figures such as Daemon Targaryen and Corlys Velaryon decide to launch a bid to control the Stepstones themselves.