The Speaker of the U.S. House of Representatives is the chamber's presiding officer and is a position that has been filled since 1789 when the U.S. Constitution specified that the House should choose a Speaker. The Speaker doesn't need to be a House Representative, but all previous Speakers have been elected Members of Congress.
The Speaker of the House is second in line of succession, should anything happen to the president, after the Vice President. The Speaker fulfils a leadership role and has to work actively to set the legislative agenda for the majority party. The Speaker also fulfils procedural and administrative functions, representing his/her Congressional district.
Election of the Speaker
On the first day of every new Congress, or after the death or resignation of the previous Speaker, the House of Representatives have to elect a new Speaker. There are usually two nominations, one from each large party. To be elected, a speaker has to win the majority of the votes.