Creative mode is the other mode that Minecraft lets you play. There is no specific goal to what you have to do, you can build whatever you want. There is unlimited blocks of each kind that you can use for your what you choose to construct. From dirt blocks to diamond armor, everything is in your inventory with no difficulty.
Picture displayed here are from creative mode inventory.
Creative mode is basically a mode where you want to have fun either by yourself or with friends. You can build with friends, have a building contest, or just build houses, and explore places were you couldn't go in survival.
In creative mode you are allowed to fly unlike survival mode. With this you can use this to your advantage make floating houses, not have to stack blocks so you can get up to a high place, and just explore the world. If your stuck in a cave you can just easily fly out rather then stack your way up with blocks for hours.
One of the great things about creative mode is that you can destroy any kind of blocks very easily, even if its obsidian or diamond. You can use this if you need to destroy a mountain instantly or destroy something that you have made.
Projects that were made easily in creative mode, harder on survival mode, that you can make as well.