Samus infiltrates the planet and begins in the Brinstar area. The planet consists of five areas - Brinstar, Norfair, Kraid's Hideout, Ridley's Hideout and Tourian. Once you begin the game, go left and jump over the large rocky terrain to find the Morphing Ball on the other side. Once you've grabbed it, roll under the rocky terrain and travel right. Head down the corridor and enter the door at the far end. Cross over the crumbling blocks in the next room and head through the door on the right. Cross the next long corridor to reach a huge shaft leading skyward.
Ascend the shaft and go through the first door you'll find on the right wall. Go past the narrow corridor to find a second giant orange shaft leading up and down. Drop down to the very bottom and go through the door there. Traverse through the next corridor until you find a Missile Tank. Pick it up and go left, back to the tall shaft. Climb back up the shaft and go through the first door on the left wall and head through the narrow corridor to go back to the first tall shaft.
Climb the shaft and go through the door up on the left. Cross the next corridor and blast the door down on the left with five missiles. Go inside to find the Long Beam. Leave and head back down to the orange shaft.
Head through the door opposite the one you entered the shaft via, then travel through the next series of long corridors filled with lava. Eventually you'll come across an Energy Tank. Grab it and move on. At the end of the corridors you'll reach a shaft leading up, so climb on up. Go through the door up on the left wall and cross the corridor inside. Blast open the door at the far side with five missiles and head inside to find the handy Bomb power-up. We'll now be heading down to Norfair, but on the way you'll be able to track the Ice Beam down.
Go back down to the long corridors, but once you reach the first small room connecting the corridors (the one with the Waver flying about below the platform), blow open a small hole in the ground six blocks along from the left door and drop down below the lava. You'll fall down to reveal a hidden shaft, descend and go through the door at the base. Cross the corridor, blow open the red door with missiles and head inside to find the Ice Beam.
Once you've gained this life-saving weapon (especially when it comes time to face the Metroids) go back out to the shaft leading up. Climb up the shaft, but once you reach the fake lava, you'll find that you can stand on the piece of lava directly below the destructible block.
You won't be able to jump up high enough to reach the platform above, so instead, aim up and shoot the block open. Immediately jump up and down four times as high as you can, on the fourth jump the block should reappear when you're within it, pushing you up to the platform above. Once you've successfully made it up (it might take a few tries) go back left to the orange shaft. Bungee down to the bottom and head through the door there.
Go through the long corridor where you found your first Missile Tank, then open the door at the end to find the room containing the elevator leading down to Norfair.