If Mario eats a Super Mushroom, he becomes a Super Mario - he grows to double his size and gains the ability to break bricks above him. Other bricks may also contain some coins or rare items so if you have enough time, try to hit them as well. There is a lot of coins scattered around for Mario to collect and special bricks marked with a question mark, which may reveal more coins or a special item when Mario hits them.
Mario should reach the flag pole at the end of each level to win the game. You are going through the Mushroom Kingdom, surviving the forces of the antagonist Bowser, and saving Princess Toadstool. In the game you are playing the role of the Mario.