Explain A and S settings to me please

tko wrote:

Quickly. You're shooting a sporting event and you know you need 1/500th of a second minimum to stop the action. What shutter speed will P-mode give you? You don't know. I don't know. No one knows.

Quickly. You're shooting your daughters portraits and the background is distracting, so you'd like F2.8. What aperture does your P-mode give you, and how do you force it to give you a constant F2.8?

Seriously. I've never used P mode in 40 years of photography. Not that they had P mode when I started.