Explanation for flat earther. This is as simple as I think I can make it.

Ok, so the black circle is the earth.  The yellow line is the light coming from the sun.  The green line is a line from the centre of the Earth to a point currently in nightime and continuing on.  The blue line is a similar line, but futher away from the point where it's the sun still only just hits the earth.  Notice how is you continue the line upwards from the Point where the green line hits surface you get to a place where you can see the sun.  Notice that the same thing happens with the blue line, but you have to go further from the surface of the earth.  This is why things high above the surface of the earth still recieve sunlight after thing things at sea level stop recieving sunlight.