This is the Forgotten Construction Yard. Destroy it to destroy the whole base, wiping it off the map and claiming all the resources contained within.
This is the Forgotten Harvester. It is always on either Tiberium or Crystals, harvesting what it can. Destroy it to gain resources gathered in the form of Crystals or Tiberium.
The Refinery will contain cash, Tiberium, and Crystals, all for the taking. Destroy it, and claim them all!
The Silo will hold precious Tiberium and Crystal resources. Destroy it to claim whatever resources the Silo holds.
The Tiberium Silo will contain Tiberium for the taking. Destroy it to claim whatever resources the Silo holds.
The Crystal Silo will contain Crystal for the taking. Destroy it to claim whatever resources the Silo holds.
The presence of a Defense HQ usually means a Forgotten base is stronger than a basic camp. Destroy this to claim some resources, in the form of Tiberium or Crystals.
This is the building that manages Forgotten defenses. Destroy it for Tiberium and Crystal resources.
This is the monetary exchange of the Forgotten. Destroy it for a quick cash bonus, which can be used in conjunction with research to buy new units!