Accessed from the Play->New engine match... menu item. This dialog enables you to configure the type of game you wish to play against the computer.
There are many sections to the Engine match dialog, here is an explanation of each:
This section allows you to choose the White and Black engines for the first game (later games may have reverse colours) and set the hash tablebases and tablebase cache values common to both engines for the match.
Optionally you may have the engine evaluation for each move added as a comment to the notation as the match is played.
Here you can set the time control for the match which both engines must adhere to.
You can set the number of games to be played in the match and whether to reverse colours after each game. Reversing colours is the most common setting since it fairly gives each engine a game with the White and then Black.
The starting position for the match can be selected, normally this is the standard opening position in chess but if the current position on screen when you selected Play-> New engine match is not the standard opening position then you can select that so shoot outs can be played with a particular position to see how the engines would play them.
Finally you can set the match title. %1 and %2 will be replaced by engine names, %n by number of games and %t by time control used.