Adolf Hitler had decided to invade Britain, but lacked the naval power to defeat the Royal Navy and provide protection for the invasion force. He therefore required the Luftwaffe to crush the RAF before turning their guns on the Navy. In August they attempted to do just that.
They began by attacking seaports to draw the fighters into that air and shoot them down. This failed because radar was able to preempt their attacks and concentrate force against the attacks.
Next the Germans turned their attention on the RAF's airfields, bombers screened by fighters pounded RAF bases in the south of England, and came close to breaking Fighter Command's resolve until Goering was ordered to turn his bombers attention to London. This was in retalliation for an attack on Berlin. During this phase, thanks to the incredible endurance of aircrew and groundcrew, the RAF ground down German airpower to the point when it was no longer able to mount daylight raids. The invasion could no longer take place

London, the airbases of Southern England, and the skys above the southern counties and the Channel. (England)