Selecting the right cameras
When choosing your cameras that you need for your application you must consider the following aspects.
Some cameras come with IR (infra-red) Illuminators that emit a bright light during the night that is not visible to the human eye. Cameras with IR will allow you to see in complete darkness.
Internal / External
Depending on where you are going to place your camera either indoors protected from the elements or outside will determine whether you need an internal or external camera. Internal cameras usually are contained within a plastic housing where as an external camera is housed in a weather resitant aluminium casing.
PTZ (Pan Tilt Zoom)
Some cameras have PTZ functionality that allows you to control moving the camera left to right (pan) up and down (tilt) and to zoom in closer. These cameras usually come with a controller pad that allows you to control the camera movements using a joystick or the camera can be connect to a PTZ compatible DVR where the camera can be controlled using a standard computer mouse.
TVL (Television Lines)
TVL is similar to resolution where it depicts how much detail the camera can produce. The more TVL the better.