The vice president supports the president. If the president is unable to serve, the vice president becomes president. The vice president also presides over the U.S. Senate and breaks ties in Senate votes.

https://www.usa.gov/branches-of-government

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The vice president of the United States presides over the U.S. Senate and takes over the role of president of the United States if the president is unable to perform their duties. If the vice president is not able to fulfill the duties of president, the role is passed to another leader in the order of presidential succession.

https://www.usa.gov/presidents.