PASM are different modes for different settings you want to control as a user.. i believe the P is automatic where the camera will take care of all settings , A is usually aperature priority mode where you will control the aperature of the pic, S is shutter speed where you control the shutter speed only and the camera controls the rest, and M is manual where you have total control of all settings .. this is what you want to use to get the settings that have been suggested ... your manual will give more info of how to achieve these settings and how to control each ...