Often at events players intend to drop from the event but don’t actually let tournament officials know. There are often several ways to drop; by writing it on the match result slip, filing out a separate drop slip or just informing the scorekeeper. Not officially dropping from the event leads to players being paired for a round and not having an opponent.
In the event that your opponent does not show up for the match you should call a staff member over as soon as the round begins. For most competitive events players receive a game loss if they are not in their seat when the match begins. (The head judge of an event can allow players a 3 min extension if he or she so chooses.) In most cases the judges that comes over will inform you that you have won game one.
At this point you will have to wait until either your opponent does in fact show up, or until 10 min have passed into the round. When either or these happens, you need to call a judge. If your opponent did show up before 10 min have passed, the judge will inform him that he will be losing game one due to Tardiness. This late coming opponent will then get the choice of whether or not to go first. Neither of you will be able to sideboard for this initial game.
If after 10 min your opponent still has not arrived the judge will then award a second game win to you, and you will have won the match. The judge should then help fill out the match slip and make sure to drop your opponent from the event. (If the opponent does eventually show up and still wants to play, he or she can rejoin the event as long as this round has not ended. they will need to tell the scorekeeper to reenter them into the event.)