Secondary fire, (MOUSE2 by default), spawns a camera that faces you or whatever you were aiming at when placing the camera.Primary fire, (MOUSE1 by default), spawns a camera.
Press and hold the menu key (Q by default), then in the tool menu in 'RENDER' select 'Camera'. This is useful for a simple security system on roleplay servers. The Camera Tool is a tool that allows the user to spawn cameras and see from their point of view through a designated key.
