2048 is a popular type of puzzle games that features a 4x4 grid where your goal is to merge tiles until you obtain the 2048 cell. Each tile has a number over it and once two similar cells collide, they merge into a tile showing the correspondent sum. 2048 6x6 is a game with similar rules, except it has a total number of 36 cells.
The app provides you with a help guide which can be accessed at any time. If it's the first time you try this type of game, I'd suggest looking for the detailed gameplay instructions within your default browser as the built-in help manual doesn't offer you much info.
2048 6x6 keeps track of your highest score which is shown on the upper side of the screen.
My only beef with this application is that it displays ads on the bottom side of the interface. One of the possible ways to get rid of these advertisements is to play the game without being connected to the Internet (disable Internet connection from Mac's System Preferences menu).
As a conclusion, I'd say you should give it a try, especially since it's free of charge.