To find the committees on Congress.gov click on Committees on the upper right corner of the homepage.
From there you can view the recent activity, the schedule, publications, and membership (takes you to a different website).
If you scroll down you can view the legislation, committee reports, communications, and the meetings. You can also use the limiters on the left to see more specific results such as Bill Type, chamber of origin, sponsor, etc.
To find committees on Govtrack, click on the Congress tab, then Committees.
Once you've selected a committee you can see members, bills, reports, subcomittees, and press statements.