If you're doing a history test on Congress then you should go to the Federal Library.
Not possible to go the Federal Library in D.C.? Check out the library's website, which includes all sorts of primary source for research. Primary sources are documents that are very close to the original. With the Federal Library, the sources are photographed or scanned (digitally copied) materials like letters, diaries, and the Constitution.
Still not sure what a primary source is? It's like when your friend writes a note to you and another friend says that it was a mean note. That's to weird to believe, right? So, what do you do? You check it out -- it's not a mean note.
That's what primary sources are. You can watch this video below for more information.