Here's a brief answer:

Before the war Polish agents passed to the British an Enigma machine, which enables the British to be aware of how it worked even if its possession did not solve the problem of how to break German codes.

Polish units and individuals escaped to the West in 1940. Many pilots joined the French Air Force and then the Royal Air Force, proving highly effective and successful from the Battle of Britain (where a Polish squadron was the most successful) onward. There were also Polish squadrons in Bomber Command.

Polish research into paratroops was passed on to the British (who had done almost no work in the area) and things like the basic parachute harness were of Polish design. Polish paras were trained and used alongside British in 1944 at Arnhem. The British raised a Polish armoured division and other army units. This division fought with distinction on the shoulder of the Falaise pocket in 1944, holding despite desperate assault by fanatical SS troops trying to break out of the Allied encirclement. Many Poles fought in Italy.

The Soviet Union, despite massacring the 1939 Polish leadership at Katyn Forest, saw advantages in raising their own Polish units, which were officered by Russians given Polish identities. The Soviet commander Rokossovssky was Polish.

In 1944 Polish nationalists rebelled against their German overseers in Warsaw, as the Red Army approached. The Red Army halted on the Vistula River and the Germans had several weeks to put down the uprising in the most brutal fashion. Stalin also resisted Western, in particular British attempts to air drop supplies and weapons to the Poles.

It is also something of a myth that the Poles fought incompetently in 1939. They did not charge tanks with massed cavalry (in Polish terrain cavalry made some sense the Red Army used cavalry divisions there in 1944), and they would have cost the Germans quite dearly had not the Soviets surprise invasion of their rear forced them into surrender. Many German units suffered grievous casualties in Poland.