Control is one of the most important parts of the Far Wilds. Each player has an area of control which is most often determined by your Buildings. Buildings give you control over any space they can see. If two players have Buildings that can see a given space that space is uncontrolled.
If you control a space that contains a Flux Well you gain control of that Flux Well.
You can see here that you control the blue area around your two buildings. Your Bone Fortress has vision 2 so has a larger radius of control then your Grove. Your Astridian Forum is also a building but it has vision of zero so doesn't expand your area of control..
When two players have buildings that can see the same space. That space is considered contested and isn't under anyone's control.
In this example the enemy just placed an Earthworks and so we lost control of the center Flux Well. Note that even though our Altar of Ix and Bone Fortress can both see the center point it only takes one enemy building to make the space contested.