Placing
From Official Barotrauma Wiki
In Barotrauma, items could not only placed inside containers or into own inventory but also placed within the environment.
Placing is possible within the submarine (e.g. for Gardening with a planter box) or within structures, e.g. in the Scan Alien Ruins missions, scanners need to be placed in special spots within alien ruins.
Usage
Prior placing the item, it must be equipped (in one or two hands) from inventory.
Once it is equipped the same gesture as with fireing a weapon or welding applies:
Holding 
right click, then target where to place it, and finally 
left clicking to place it, e.g. on any empty space on the background wall's grid.
