For most UCI researchers, ProQuest Congressional is the best source for both: 1) locating hearings when you already know the date or the committee, and 2) searching the full text of published and unpublished hearings. Other sources can be useful if you are off campus or are looking for a different type of media (like video from C-SPAN.)
Senate and House Committees also make transcripts and video of hearings available on their websites. For recent hearings, try finding the committee's site with Google or another major search engine.
A hearing is a meeting of a Senate, House, joint, or special committee convened to solicit opinion on proposed legislation, conduct an investigation, evaluate a department, assess a law, or gather other information of interest. Most congressional hearings are public. Official transcripts are usually available within two months to two years.
See Bluebook Rule 13.3. Example: