Did Congress declare war?

Yes. By joint resolution. Here are the details.

2001 S.J. Res. 22; 107 S.J. Res. 22

Considered in the Senate, 09/12/01 Passed in the Senate, 09/12/01

2001 H.J. Res. 61; 107 H.J. Res. 61

Considered in the House, 09/13/01 Passed in the House, 09/13/01 

Presented to the President , 09/13/01 

Became Public Law (P.L. 107-39) , 09/18/01

In relevant part, it provides:

(6) thanks those foreign leaders and individuals who have
expressed solidarity with the United States in the aftermath of the
attacks, and asks them to continue to stand with the United States in
the war against international terrorism;

(7) commits to support increased resources in the war to
eradicate terrorism;

(8) supports the determination of the President, in close
consultation with Congress, to bring to justice and punish the
perpetrators of these attacks as well as their sponsors

Note that this includes the use of force against terrorists and their sponsors.