The Salvage Shop is a special shop that can only be accessed by successfully completing certain portal missions
The salvage shop is the only place where you can earn new building blueprints. By clicking the large chest in the middle of the shop you will initiate a battle. If you are victorious you will receive a building blueprint that can be used to build any number of that type of building.
You can also use the salvage shop to buy units and items With salvage. It is possible to preview the item or unit's stats before you buy it by clicking directly on it.