The main job of the Legislative Branch is to pass laws. This branch of government also originates spending bills and approves... The main job of the Legislative Branch is to pass laws. This branch of government also originates spending bills and approves treaties. The Legislative Branch is made up of the House of Representatives and the Senate. Together, these two entities form the Congress. Congress has specific authorities, such as declaring war and rejecting presidential appointments. The House of Representatives consists of 435 members and the Senate has 100 members.