Aperture Priority Mode
(often it has a symbol of ‘A’ or ‘Av’)
In this mode, you as the photographer set the aperture that you wish to use and the app makes a decision about which shutter speed is appropriate in the conditions that you’re shooting in. To go into aperture priority mode, you need to tap on the shutter time section in the app. Then, you will be able to set the aperture you wish to use:
Shutter Priority Mode
(often has a symbol of ‘Tv’ or ‘S’)
In this mode, you as the photographer choose the shutter speed that you wish to shoot at and let the app make a decision about which aperture to select to give you a well-exposed shot. To go into shutter priority mode, you need to tap on the aperture section in the app. Then, you will be able to set the shutter time you wish to use.
Shutter and Aperture Priority Mode (sometimes referred to as "Manual" Mode)