Summary: all equipment, resources, and most marine activities, depend upon structures, selected and placed by the commander. Placed structures must be built by marines.
To get an overall picture, see the tech tree.
Turrets and Siege Turrets Though constructed like structures, turrets and siege turrets are weapons, and so listed in the weaponry section.
Sentry Turret
Cost
16 rps
Build time
30
Armor Pts.
1000
Siege Turret
25 rps
50
2000
To get an overall picture, see the 
Cost 
Build time
Armor Pts. 