The PLex Reycler is used for refining minerals. youll have to place it on a planet, astroid, or space station.
Once it is placed, activate it by pushing r, it should open up your inventory and its own, your inventory is the top portion. Drop your first stack of minerals into the recyler and there should be an ok button of some sort, it will then take your stack of lvl 1 2 3 or 4 and refine them to the next level if you have enough minerals.
Doors can be placed on any object stationary or ship. fill your hallway with door modules and when your in first person they can be opened or closed by pushing R if you are close enough, it will say "activate doors with R" or somthing to that degree