The purpose of a conference committee is to iron out the differences between bills that are passed by the two Houses of Congress.
The United States Congress is, of course, made up of two Houses. These are the House of Representatives and the Senate. For a bill to pass the Congress, it must be approved by both of these Houses. The bills that are approved by the two Houses must be identical.
Although both Houses of Congress have to approve any bill, they can each create different versions of the same bill. We have seen this process in 2013 where the House of Representatives has passed bills to fund the government but have attached provisions meant to weaken “Obamacare.” When these bills have reached the Senate, that House has passed them without the Obamacare provisions. Because the bills are not identical, neither of them passes Congress.
A conference committee can be appointed to iron out differences between the bills passed by the two houses. There are members from each house on these committees. If they can agree on a bill, that bill is sent back to the two Houses (now in identical form) to be voted on.