A is the area that is radiating, ie the surface area of the whole sun (4π
e (or ε) is the emissivity
factor, always less than 1, because the sun is not a perfect black body radiator …
I don't know where to find the value of ε.
That gives you the total
radiated power …
at the earth's surface, that covers the whole sphere round the sun at the distance of the earth, so you have to divide by the surface area of that sphere, and multiply by the area of the bit of earth you're interested in (usually 1 square metre).