What is the next step in Minecraft?

Techinically there is no 'next' step - Minecraft is a sandbox game. You do whatever you want.

The world you are in at the moment is called the 'Nether' - it is filled with Netherrack, Gravel, Glowstone, Soulsand, Lava and a randomly spawning structure called a 'Nether Fortress'

The Nether Fortress is made out of a material called 'Netherbrick' which is a darker colour than Netherrack. In a future update you can make Netherbrick by smeling Netherack.

A typical Nether Fortess: http://images2.wikia.nocookie.net/__cb201112221804...

A Nether Fortress is the only place where a creature called a 'Blaze' can spawn. They will spawn at special Blaze spawners in the Nether Fortress: http://images4.wikia.nocookie.net/__cb201201171630...

When killed they will ocasionally drop a 'Blaze rod'. This can be used with 3 cobblestone to create a brewing stand (you can make potions) or crafted into 'Blaze powder' by placing it in your crafting table.

(you can also find 'Nether wart' in the fortress, it grows on Soulsand in one of the rooms. It is the basis for all potions.

Back the the overworld a mob that you will see spawning is the 'Enderman' - a 3 block tall black, teleporting mob with glowing eyes. If you kill it there is a chance it will drop an 'Enderpearl' If you throw this you will teleport to wherever you land. If you combine it with a Blaze Powder however, it wil become an 'Eye of ender'.

You will need to collect PLENTY of these - I'd say 15 at the very least.

When you right click with one it will fly off into the air (it may break before it falls, it may not - you'll need a few). This indicates which direction an 'Ender portal' is in.

A filled Ender portal: http://media-mcw.cursecdn.com/thumb/d/df/Screen_sh...

You will have to dig to reach the portal, but it will ALWAYS be within a 'Stronghold' and always in the OVERWORLD, not the nether.

Once you get there you will find that the place is full of loot and a mob called a 'Silverfish' They aern't hard to kill but there are a lot of them - scary.

If you fill the portal with Ender eyes it will appear as above, if you jump through you will get to face the Boss, the 'Ender Dragon' in a place called the end. Here the only other spawning mob is the endermen and you get a new block - End Stone (its decrotive, no use)

Tutorial on defeating the Ender Dragon: http://www.youtube.com/watch?v=4SaDKbkk8hI

(I reccomend you bring your weapons enchanted and with very good armor. A pickaxe, spare weapon. DEFINETLY A BOW. If you wear a pumpkin on your head endermen will not attack when you look at them.)

After this you have the wither - but that isn't the next step. Little tip though, if you go past this and spawn it after your own reseach, don't spawn it in your house.

^-^ Hope this helps! ^-^

I think you have to find a stronghold in the Nether and go kill an ender dragon. I haven't played Minecraft in a world, but I think that's it. If not, you should try the Minecraft wikia.