A Bill is debated on the floor and then sent to committee(s) for revisions. Hearings are held, with testimony from interested parties; Prints are reports or studies prepared for the use of a committee, often by the Congressional Research Service (CRS); and Reports are issued containing the revised bill, committee's recommendations and background information. Reports can also be issued as a result of investigations by Congress.
Once revised, a bill is brought again before the House or Senate for approval. The bill may then be referred to a conference committee to reconcile differences in similar bills in both Chambers. Conference committees are composed of members of both the Senate and the House.
Documents (Senate & House) are usually communications from the Executive Branch. They can include reports of Executive Departments and Agencies, often submitted in accordance with Federal law.
Senate Treaty Documents contain the texts of treaties submitted to the Senate by the President for ratification.
Senate Executive Reports are reports of the Committee on Foreign Relations relating to treaties which have been submitted to the Senate for ratification. They can also be reports of various Senate Committees regarding the nomination of persons for Federal positions.