Dates of World War 1 and two

The First World War began on 28th July 1914 when the Austro-Hungarian Empire invaded Serbia starting a vast chain of alliances. Great Britain (of which England is a part) declared war on Germany on the 4th of August, entering the war so for the British it starts then.

The armistice took effect on the 11th of November 1918, which normally counts as the end date, and the final treaty officially ending the war was signed on 28 June 1919 by Great Britain. Technically peace with Turkey wasn't signed until 1924 since the dust had to settle on the break up of the Ottoman Empire.

The Second World War wrapped in several seperate ongoing wars under it's banner the first of which began as a war in Asia between China and Japan in 1937, but it is generally held in the United Kingdom (Great Britain) to have begun on the 3rd of September 1939 with a declaration of war on Germany (again!), after the Germans had invaded Poland on the 1st of September. The Poles, understandably, date it from the 1st!

The Germans surrendered on the 7th (taking effect on the 8th) of May 1945 although isolated units fought on for a few more days against the Russians.
The war with Japan was ended by surrender on the 15th of August, although it took until the 2nd of September to make it offical. The War is thus considered to have ended by all parties on the 2nd September 1945.

So for Great Britain the Wars are:
4th Aug 1914 to 11th Nov 1918 and
3rd Sep 1939 to 2nd Sep 1945

Other countries have various shifting dates to reflect their own entry and exit from the wars.