Once the archer queen altar is build you have access to the archer queen. The archer queen can defend your village or you can attack other villages with her.
Most people place the archer queen altar close to their town hall. This way she defends the town hall when an enemy comes close to it. But people who farm a lot mostly place the archer queen altar close to the resources to defend those.
Archer queen altar building cost
|Cost||Build Time||Hitpoints||Unlocked Unit||Size||Town Hall Level Required|