Do people use the suns radiation source for anything? if so, what?

Yes, there are a few minor things that people use the sun's radiation for.

-- warming the Earth, so that the temperature outside is usually warmer than  300 degrees below zero;

-- warming the ground, so that the water doesn't freeze solid;  that way, rivers can flow, oceans and lakes can evaporate and reload the rain, and the faucets and toilets in our houses work right;

-- warming the atmosphere, so that the Oxygen and Nitrogen don't turn soupy, or freeze solid;

-- making the Earth light during the daytime, so that we can walk around without banging into stuff, and drive around without keeping our headlights on all the time;

-- This is the big one:  Plants LIVE and GROW on the sun's radiation, which is very lucky.  If plants didn't live and grow, then we would have no tobacco, no lettuce, no onions, no peppers, no tomatoes or celery or potatoes.  And no steak or milk or hamburgers either, because cows live on plants.

Without the sun's radiation, the Earth would be pretty much a dark frozen rock with a thin covering of ice or dirt in a few places.