Final answer:
The Vice President presides over the Senate and has the power to cast a tie-breaking vote. In their absence, the President Pro Tempore leads the Senate.
Step-by-step explanation:
The Vice President of the United States has specific roles defined by the Constitution. One key role is their duty to preside over the Senate. The Vice President generally does not vote on legislation but holds the unique power to cast a tie-breaking vote if the senators are evenly split on a bill or nomination. Furthermore, in the event that the Vice President is not available, the President Pro Tempore takes over the duty of leading the Senate. The Vice President is often seen as a figure of lesser influence in daily operations, but they play a critical role in the legislative process and in the line of presidential succession.