>>4373115A(perture) lets you control your aperture and ISO, the camera adjusts the shutter speed until it reaches your set exposure value.
With this you can isolate the subject using depth of field, or get optimal sharpness from your lens. Best for stills.
I almost always shoot in this mode unless I want to do some gimmick stuff.
S(hutter) lets you control your shutter and ISO, the camera controls the aperture to reach your set EV.
This is for moving subjects or something moving around the subject and lets you choose if you want to freeze that motion in sharp image or let it become a soft blurry veil.
P(rogram) lets you control ISO, the camera controls shutter speed and aperture to reach your set EV.
This is pretty much auto mode but doesn't fuck with your metering or focus.
It's if you need to act fast or hand the camera to a noob while not trusting the auto mode
M(anual) lets you control all aspects of your exposure triangle (Aperture, shutter, ISO) with the EV only serving you as guide.
People will tell you that this is the cool kid's mode that should always be turned on no matter what and that is true for beginner's since you will learn what is important the hard way, by fucking up photos.
When you know what you are doing, you can let the camera do some work for you.
If you can take your time and want the perfect photo, you use this mode.
All these modes are useless if you chose the wrong metering mode though.
