Instructions
Research Perdition Turrets at the Hyperion lab anytime after you have completed Mission 2.2 "The Devil's Playground" and reached level 10 for Zerg research. Perdition Turrets are Zerg Tier II technology and become to research available after this mission.
Click on any of your available SCV units once the research is complete. Click the "Basic Buildings" option on the unit. This brings up a list of buildings you can have the SCV build.
Click the "Perdition Turret" option. Move th emouse to the location around your base where you want to build the turret and click to have the SCV build it.