Thinktanks are research institutions that produce analyses of current or future societal issues. Housing policy, income taxes, debt, credit and international trade are just some of the issues you'll see covered by these research institutions.
Some thinktanks have a political agenda while others are nonpolitical.
I have collected a list of some of the best-regarded thinktanks here. Usually, there's an emphasis on economics.
Learn how to use statistics and make arguments. Or learn to criticize their use in an argument!
Can you use thinktank papers in your project? It depends on the professor. The real point, as stated above, is to get you to see how arguments on contemporary issues are constructed.