The Belair X 6-12 is an auto-exposure camera. This means you will need to set the correct film sensitivity so that the camera exposes correctly. The ISO/ASA dial is located behind the lens board, under the battery chamber.
Auto Exposure Mode: The camera will expose correctly according to ISO you selected. Select and turn the ISO Dial so that it matches the ISO of the film you are using.
B (Bulb) Mode: The camera will expose as long as you press the shutter: switch to B mode, hold the Shutter Release Lever for as long as you want to expose the film.