Enumerated powers are powers that are explicitly given to Congress in the US Constitution. The following two powers are some of the most important to Congress.
1) Declare War- The president cannot declare war without the approval of Congress. Essentially, the president must ask Congress for the permission to declare war.
2) Regulate commerce with foreign nations- This allows Congress to develop trade relations with other countries. This is especially important in today's society, as the United States is constantly importing and exporting goods/resources from all over the world.