The charm of Minecraft is in its crude, blocky graphics. As you wander about a seemingly empty map, you soon learn to use your trusty pickaxe to chisel away the environment around you. Doing so not only allows you to rebuild the entire map as you see fit, but can also throw up a number of interesting surprises.
Create buildings, caverns, landmarks.. you're only limited by your imagination. If you like, you can invite a bunch of friends along to help you build a masterpiece worthy of showing the entire world. But be quick about it, because at night monsters come out to play, so you need to make sure that you have made preparations for you (and your friends) to stay safe until dawn.