The Legislative Branch
The legislative branch, or Congress, includes the House of Representatives and the Senate. A legislature with two chambers is known as a bicameral legislature. Because both the House and Senate have to pass a bill in order for it to become law, they are able to check and balance one another, adding to the Constitution's safeguards against a too-efficient government, which could more easily achieve its objectives.
Congress has many specific powers, including the power to raise revenue, to provide for America's defense, to borrow money, to regulate commerce between the separate states, to determine how immigrants may be naturalized, to coin money, to create post offices, to promote science and "useful arts" by protecting inventors' patents, and to declare war. More broadly, Congress has the power to promote the "general welfare" and to make "all laws which shall be necessary and proper" to achieve its legitimate ends.
If Congress passes a bill, but the president vetoes it, Congress can override that veto, passing the bill over the president's objection if a two-thirds majority in both the House and the Senate votes to do so.