MASH is a fairly common fortune telling game played by children. It stands for Mansion, Apartment, Shed, House (although shed is highly debatable, and is often replaced with swamp, shack, sewer, or street), those being the four options for where someone might live. The game continues on to give you an extensive description of your life in the future.
In order to play, you will need a pen, some paper, and, if possible, a friend. You start by picking a number of categories that you feel might be important to your future -- where you might live, who you might marry, number of kids, what car you might drive -- and both players contribute a number of possible options. Some rule-sets prescribe four options for each list, some say three per player; it doesn't really matter, although the fact that the name of the game provides four options does give you a strong hint as to the most common choice. It is common, although not universal, to choose a range of options including at least one great option, one terrible option, and one okay option. It is also common to include one silly/crazy answer, although the title fails us here.
Once your lists are completed, you will have to pick a random number. The most common way to do this is have one player start drawing a spiral on the paper, and the other player telling them when to stop; one then draws a line across the spiral, and counts how many times the line intersects with the spiral. This provides the 'magic number'. Alternatively, you can have one player make tic marks, write random numbers, roll a die, or whatever else you may feel.
For each list you then count off the items, crossing off an item when you reach the magic number. When you reach the end of the list, you cycle back to the top of the list, and keep crossing items off until you have only one remaining option: that is your true fate. Move onto the next list.
In researching this, I found that a surprising number of people have quite serious questions about this game. In almost every case, the answer is "if you want to, sure." The International M.A.S.H. Federation, the controlling body for maintaining MASH rules and standards, has remained obligingly imaginary, giving players a tremendous amount of latitude in gameplay.
MASH has been around since at least the 1950s, and has spread around the world. It occurs in many different versions under many different names, but MASH seems to be consistently the most common, and is becoming more standardized with the advent of the internet. It is now possible to download pre-formatted MASH sheets, play MASH online, or download MASH apps. Regardless, this is a game that is entirely dependent on spirit of those playing it, and will continue to evolve to meet the needs of those playing it.