We elect a President for how many years?
In the United States, a President is elected for a term of four years. This is outlined in Article II, Section 1 of the U.S. Constitution.
The process of electing a President is quite complex. It involves primaries and caucuses, state and national conventions, and the general election campaign. The Presidential election itself is an indirect one. Citizens vote for electors, who are part of the Electoral College, and these electors then vote for the President.
Notably, the U.S. Constitution, specifically the 22nd Amendment, also limits a President to two elected terms in office. The amendment was ratified in 1951 in response to President Franklin D. Roosevelt's four terms in office. There's an exception that allows a Vice President who assumes the Presidency due to death, resignation, or removal of the President, and serves two years or less of the former President's term, to be elected for two additional full terms.
The purpose of this term limit is to prevent any one person from holding too much power for an extended period of time. The four-year term and the limit of two terms attempts to balance the need for continuity and experience with the desire to prevent the concentration of power and maintain a degree of democratic control.
After a President is elected in November, they are inaugurated and officially begin their term on January 20th of the following year.