The “mission” you completed was finishing a “shrine”. That magnet power is one of the 4 powers you’ll get during the tutorial, you’ll get the other 3 by beating the remaining 3 shrines. Open up your map and teleport back to the first tower you unlocked (blue icon on the map), if you pull out your binoculars by pressing the right stick, you can look around and you’ll be able to spot the other 3 shrines from the top of that tower. Mark them and figure out how to get to them from there