The Monday after the second Wednesday in December of U.S. presidential election years is set as the date on which the electors meet and vote. In 2020, the meeting is on December 14.
Electoral college delegations meet separately in their respective states and the District of Columbia at places designated by their state legislatures. The electors vote by paper ballot, casting one ballot for president and one for vice president. The electors count the results and then sign six certificates, each of which contains two lists, one of which includes the electoral votes for the president, the other, electoral votes for the vice president, each of which include the names of persons receiving votes and the number of votes cast for them. These are known as Certificates of the Vote, which the electors are required to sign. They then pair the six Certificates of Ascertainment provided by the state governors with the Certificates of the Vote, and sign, seal and certify them. The six certificates are then distributed by registered mail as follows: (1) one certificate to the president of the U.S. Senate (the vice president); (2) two certificates to the secretary of state (or equivalent officer) of the state in which the electors met; (3) two certificates to the archivist; and (4) one certificate to the judge of the U.S. District Court of the district in which the electors met.
Information from the Congressional Research Service