23rd

Section 1. The District constituting the seat of Government of the United States shall appoint in such manner as the Congress may direct:


A number of electors of President and Vice President equal to the whole number of Senators and Representatives in Congress to which the District would be entitled if it were a State, but in no event more than the least populous State; they shall be in addition to those appointed by the States, but they shall be considered, for the purposes of the election of President and Vice President, to be electors appointed by a State; and they shall meet in the District and perform such duties as provided by the twelth article of amendment.

Section 2. The Congress shall have power to enforce this article by appropriate legislation.

 
This amendment is the one that appropriates the electoral college candidates for the District of Columbia.
 
The electoral college
 
This website has information on the electoral college. What it does, who is apart of it, when it was started, etc. Take a look and learn a little bit more about the processes of the electoral college.