Read Operation Sea Lion. Germany intended to invade Britain but first they had to overcome our naval presence in the British Channal, North Sea and Irish Sea. Our navy was impressive and wasn't easy to take down. Secondly they had to take down our air superiority. We might have been out numbered, but we had a lot more men with flying experience and much better planes. Two things that the Luftwaffe did not have. Thirdly, they had to decide which was more important. Concentrating their efforts in taking over the UK or expand eastward and take over Russia. If successful, they would come back and easily take the UK since we would have no eastern allies.
They attempted to take Russia under the operation name Barberossa. Many historians believe Operation Barberossa was Hitlers downfall.