I know they gave massive amounts of funding to Europe, but what was actually done with all of this money other than reconstruction? Is it generally analyzed as the sole reason for Europe's quick recovery?
The money did go mostly towards rebuilding, but rebuilding had some side effects. With the rebuilding of Western Europe, this brought jobs back to Europe. Along with money, the United States also sent millions of dollars of aid, such as food, medicine, and equipment. Along with aid and cash, volunteers were sent. Doctors came to treat the sick and injured, and other specialists came as well.
This cooperation between Europe and the United States allowed their relationships to blossom. This close relation allowed them to create formidable alliances, like the North Atlantic Treaty Organization (NATO).
In a way, this aid also allowed military power of Europe to grow. With economies and industrial output expanding, the countries of Western Europe could afford more weaponry to defend themselves.
The Marshall Plan allowed European economies to be "brought back to life" after World War 2. Without the Marshall Plan, recovery would have taken much longer.
You can read more about the Marshall Plan here - https://history.state.gov/milestones/1945-1952/marshall-plan
And here - http://marshallfoundation.org/marshall/the-marshall-plan/history-marshall-plan/
Its impact has been overrated in the past. The money given over the ERP's duration totalled perhaps 3% of the GDP of recipient countries: important rather than decisive, and certainly not the sole reason for growth. By tying aid to purchases from the US, some of it amounted to a subsidy to US producers and shippers, sometimes preventing imports from cheaper suppliers. The plan facilitated trade by easing western Europe's late-1940s dollar shortage, lessening trade barriers, easing transactions through the EPU and encouraging an international approach to the region's needs. It certainly assisted with overcoming immediate shortages, but reconstruction was mostly (and inevitably given its scale) a European-financed affair. And Europe paid a price in the continent's deepening division, now not merely ideological but also economic and commercial. Contemporary publicity played up the plan as a symbol of Atlantic solidarity in the opening stages of the Cold War, but the numbers don't live up to the propaganda. It was a limited but effective stimulus, not a bailout.