system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What is a think tank and what do they do?

In political news stories you often see mentions of "think tanks" that lean either left or right.  I'm curious what exactly a think tank is.  How are they formed?  How are they funded?  What do they do?
gpt
Think tanks are a specific kind of lobbyist organizations that advocates for certain things by employing university level academics to write white papers, policy documents and model legislation. These documents are, of course, the same documents that governments themselves prepare as part of the legislative process, and think tanks contribute their documents to relevant governments free of charge in the hope that the government will adopt the think tank version in whole or in part, rather than writing their own version. 

Obviously, as a type of lobbying organization, they may be general purpose and lean towards a broadly leftist or rightist agenda, or they may be single issue or specialist focus in which case they may not really align fully with either party. But they will almost certainly have some viewpoint that they are pushing for. 

Like all lobbying organizations, they get started by various people or organizations that want to lobby for a particular viewpoint and who like the think tank model. They are also funded in a whole variety of ways, some by various industries, some by various individuals or foundations, some by political parties, and some are even partly publicly funded.