Answer by taking a quote from the following article:

John Maynard Keynes, 1st Baron Keynes  ( KAYNZ; 5 June 1883 - 21 April 1946), was a British economist whose ideas fundamentally changed the theory and practice of macroeconomics and the economic policies of governments. He built on and greatly refined earlier work on the causes of business cycles, and was one of the most influential economists of the 20th century and the founder of modern macroeconomics theory. His ideas are the basis for the school of thought known as Keynesian economics, and its various offshoots. During the Great Depression of the 1930s, Keynes spearheaded a revolution in economic thinking, challenging the ideas of neoclassical economics that held that free markets would, in the short to medium term, automatically provide full employment, as long as workers were flexible in their wage demands.

The British Government called on Keynes's expertise during the First World War. While he did not formally re-join the civil service in 1914, Keynes travelled to London at the government's request a few days before hostilities started. Bankers had been pushing for the suspension of specie payments - the convertibility of banknotes into gold - but with Keynes's help the Chancellor of the Exchequer (then Lloyd George) was persuaded that this would be a bad idea, as it would hurt the future reputation of the city if payments were suspended before it was absolutely necessary.  In January 1915, Keynes took up an official government position at the Treasury. Among his responsibilities were the design of terms of credit between Britain and its continental allies during the war, and the acquisition of scarce currencies. According to economist Robert Lekachman, Keynes's "nerve and mastery became legendary" because of his performance of these duties, as in the case where he managed to assemble - with difficulty - a small supply of Spanish pesetas.  The secretary of the Treasury was delighted to hear Keynes had amassed enough to provide a temporary solution for the British Government. But Keynes did not hand the pesetas over, choosing instead to sell them all to break the market: his boldness paid off, as pesetas then became much less scarce and expensive.  On the introduction of military conscription in 1916 he applied for exemption as a conscientious objector, which was effectively granted conditional upon continuing his government work.  In the 1917 King's Birthday Honours, Keynes was appointed Companion of the Order of the Bath for his wartime work, and his success led to the appointment that would have a huge effect on Keynes's life and career; Keynes was appointed financial representative for the Treasury to the 1919 Versailles peace conference. He was also appointed Officer of the Belgian Order of Leopold.  During the Second World War, Keynes argued in How to Pay for the War, published in 1940, that the war effort should be largely financed by higher taxation and especially by compulsory saving (essentially workers lending money to the government), rather than deficit spending, in order to avoid inflation. Compulsory saving would act to dampen domestic demand, assist in channelling additional output towards the war efforts, would be fairer than punitive taxation and would have the advantage of helping to avoid a post war slump by boosting demand once workers were allowed to withdraw their savings. In September 1941 he was proposed to fill a vacancy in the Court of Directors of the Bank of England, and subsequently carried out a full term from the following April. In June 1942, Keynes was rewarded for his service with a hereditary peerage in the King's Birthday Honours. On 7 July his title was gazetted as "Baron Keynes, of Tilton, in the County of Sussex" and he took his seat in the House of Lords on the Liberal Party benches.  As the Allied victory began to look certain, Keynes was heavily involved, as leader of the British delegation and chairman of the World Bank commission, in the mid-1944 negotiations that established the Bretton Woods system. The Keynes-plan, concerning an international clearing-union, argued for a radical system for the management of currencies. He proposed the creation of a common world unit of currency, the bancor, and new global institutions - a world central bank and the International Clearing Union. Keynes envisaged these institutions managing an international trade and payments system with strong incentives for countries to avoid substantial trade deficits or surpluses. The USA's greater negotiating strength, however, meant that the final outcomes accorded more closely to the more conservative plans of Harry Dexter White. According to US economist J. Bradford DeLong, on almost every point where he was overruled by the Americans, Keynes was later proved correct by events.  The two new institutions, later known as the World Bank and the International Monetary Fund (IMF), were founded as a compromise that primarily reflected the American vision. There would be no incentives for states to avoid a large trade surplus; instead, the burden for correcting a trade imbalance would continue to fall only on the deficit countries, which Keynes had argued were least able to address the problem without inflicting economic hardship on their populations. Yet, Keynes was still pleased when accepting the final agreement, saying that if the institutions stayed true to their founding principles, "the brotherhood of man will have become more than a phrase."  In the late 1930s and 1940s, economists (notably John Hicks, Franco Modigliani, and Paul Samuelson) attempted to interpret and formalise Keynes's writings in terms of formal mathematical models. In what had become known as the neoclassical synthesis, they combined Keynesian analysis with neoclassical economics to produce neo-Keynesian economics, which came to dominate mainstream macroeconomic thought for the next 40 years.  By the 1950s, Keynesian policies were adopted by almost the entire developed world and similar measures for a mixed economy were used by many developing nations. By then, Keynes's views on the economy had become mainstream in the world's universities. Throughout the 1950s and 1960s, the developed and emerging free capitalist economies enjoyed exceptionally high growth and low unemployment. Professor Gordon Fletcher has written that the 1950s and 1960s, when Keynes's influence was at its peak, appear in retrospect as a golden age of capitalism.  In late 1965 Time magazine ran a cover article with a title comment from Milton Friedman (later echoed by U.S. President Richard Nixon), "We are all Keynesians now". The article described the exceptionally favourable economic conditions then prevailing, and reported that "Washington's economic managers scaled these heights by their adherence to Keynes's central theme: the modern capitalist economy does not automatically work at top efficiency, but can be raised to that level by the intervention and influence of the government." The article also states that Keynes was one of the three most important economists who ever lived, and that his General Theory was more influential than the magna opera of other famous economists, like Adam Smith's The Wealth of Nations.

How did he want currency managed?
He proposed the creation of a common world unit of currency, the bancor, and new global institutions - a world central bank and the International Clearing Union.