What do congressman typically serve on two or three of these while in Congress?

Members of Congress typically serve on two or three Committees.

The Standing Committees of the House of Representatives are:

Agriculture, Appropriations, Armed Services, Budget, Education and Labor, Energy and Commerce, Financial Services, Foreign Affairs, Homeland Security, House Administration, Intelligence (Permanent Select), Judiciary, Natural Resources, Oversight and Government Reform Rules, Science and Technology, Small Business, Standards of Official Conduct, Transportation and Infrastructure, Veterans' Affairs, Ways and Means, (Whole)

Standing Committees of the US Senate are:

Aging, (Special) Agriculture Nutrition and Forestry, Appropriations, Armed Services, Banking, Housing, and Urban Affairs, Budget,Commerce, Science and Transportation, Energy and Natural Resources, Ethics (Select), Environment and Public Works,Finance,Foreign Relations, Health, Education, Labor, and Pensions Homeland Security and Governmental Affairs, Indian Affairs, Intelligence (Select), Judiciary, Rules and Administration Small Business and Entrepreneurship, Veterans' Affairs