The Kir'shara artifact lets a ship line up several hostiles in the same system and attack them one after another automatically, instead of manually re-targeting after every kill. Once activated, the artifact queues your chosen targets in order and the ship works through them in sequence -- it applies to Wave Defense targets as well as regular hostiles. An icon appears next to any hostile that's currently in your queue, so you can see at a glance what your ship is committed to.
A ship running the Kir'shara queue can't do anything else -- no moving within the system, no activated abilities -- until it finishes its current attack sequence, though you can still add hostiles to the queue as slots open up. If another player destroys a hostile you'd queued, your ship frees that slot and moves on to the next target rather than stalling. To cancel the whole sequence, just order the ship to move elsewhere without attacking. Upgrading the artifact's level increases how many hostiles it can hold in queue at once, which matters more the deeper you get into hostile-dense systems. One catch worth knowing: you need to stay active in the app for the queue to keep running, though you're free to switch to other game screens in the meantime -- just don't background the app entirely.