The appointment and confirmation of Justices to the Supreme Court of the United States involve several steps set forth by the United States Constitution.
The President of the United States nominated Merrick Garland on 3/16/2016. He now must face a series of hearings in which both the nominee and other witnesses make statements and answer questions before the Senate Judiciary Committee, which can vote to send the nomination to the full United States Senate. Confirmation by the Senate allows the President to formally appoint the candidate to the court.
This can only happen if Mitch McConnell does what the Constitution is asking him to do and what We The People are paying him for. If he refuses, he should resign immediately.