You will need a utility like WinRAR , 7-Zip , or The Unarchiver to open and extract the contents.
The file appears to be a compressed archive containing the game Monster Outbreak , a 2D pixel-art survival game. Game Overview Genre: Survival, Tower Defense, Action RPG. Developer: GameMunchers. Monster.Outbreak.rar
Usually found on gaming forums or community boards. You will need a utility like WinRAR ,