As you arrive on the planet, you will land your spacecraft in a convenient open area called Crateria (like a crater). Save your game now to avoid any mishaps (press down while standing on the top of the spaceship). Run to the left, shoot the door and enter. You will notice little bugs around, they are the butterfly's of Zebes. Continue to the left (hop over the mound) and then down the pit to the very bottom. Jump over the blue door, hold down and fire to open it (or aim diagonally down and fire).
Upon entering you should notice the blue clouds floating around, signifying the desertion of the area (also note the cracks on the tiles and walls); this is obviously an old place.
Make your way to the bottom of this tall room (stay to the far right as much as possible, there's a hole that will allow you to fall about half way) and continue through the door to the right. As you enter, you'll notice that the door behind you becomes gray (it has been disabled and you cannot exit). Also note that you are standing where Mother Brain was defeated originally, jinkies! Continue to the far right, and head through the blue door; use the elevator pad and travel downwards. You will travel down a large tube and find yourself in the starting area of the original Metroid game! Make your way to the left (the right is a dead-end), hop up the steps and fall down the hole. Jump up and grab the Morph Ball; press to continue after the music ends.
The world immediately springs to life; the eye on the wall to your left will open and shine light wherever you move (within a certain range of it) and the two little faces near the podium will illuminate and turn to face towards it.
It's time to leave, so move to the right; you can't normally jump up the way you came in but it is possible to wall jump it. Notice the little block at the bottom of the podium, it's blocking your way so duck and shoot it to destroy it. Morph into a ball ( ) and continue to the right. Press jump or up to get out off the Morph Ball mode.
Missile Upgrade #1
From the elevator, move to the far right, and head through the blue door. You can't go through the pink door (you must use a missile to unlock it). Notice the cracked blocks, you can shoot at them diagonally or from up above to destroy them and then continue down. Morph into a ball, head towards the blue door on the left and then change back and head through.
You are now in a Chozo area, notice the ground and walls, this is uniform for almost every Chozo area. Shoot the glowing orb it is holding to reveal a missile upgrade; jump up and touch it. After the music stops, press Start to continue. Missiles are now enabled! Press to enable the missiles, notice the barrel of your arm cannon opens to signify the change in weaponry. Do not waste ammo now, continue back out the door you came in.
Roll to the right, head upwards, jump on the first block platform, and fire straight up. Jump up, morph into a ball on your way up and continue to the right (this might take some practice, but go ahead and do so now, you'll need the skill).
Select your missiles, fire all five at the pink door to unlock it permanently (you will never have to waste another five on that door), continue to the right.
Missile Upgrade #2
In this long hallway, run to the far right, morph, hop up and grab the missile upgrade (you now have a maximum capacity of 10).
Continue back to the left, through the door, across the cracked blocks and through that door. Now head back up the elevator shaft (notice the faces turn towards you as you move upwards).
As you arrive back in the chozo-like area, it is now lighted and much more warm, as you'll soon understand.
A Hostile Presence
Head through the door. Immediately you'll be introduced to your first foes: Space Pirates. Use one (1) shot to take them out. Note that they can leap off of walls and fire lasers from their forehead, eyes and chest.
Make your way to the left, killing any that get in your way (probably all to be safe). You may notice objects that appear after their destruction, these will be either ammo or health. Health look like pulsating purple circles and ammo will either look like missiles or metal orbs (power bombs, later on).
Go through the previously locked door, it's flashing gray/blue. Make your way back up the long room, kill all of the mantis-bots (they will probably be an annoyance if you don't, falling here is a real pain). They are easy to dispatch of if you jump up from below, and fire at their feet to avoid any lasers.
After you make it to the top, head through the blue door. Now that the world is "alive," monsters roam it. You immediately see a ground scrub guy, who simply runs around the edges of the room, it only takes one hit to kill and is easily avoidable (but killing is often the better choice, since they may follow you around a room and cause problems).
Head up, ignore the first blue door on the left (you need morph ball bombs for that), and go through the pink door on the right. Move to the right, destroy the little fly bugs (1 hit kill) and the yellow ceiling guy (4 shots), and continue to the right and through the door.
Map Station #1, Crateria
Move to the right and run into the map station, you'll attach your arm into the device and collect all of the general map data for this area of the world.
You will then be taken to the map screen (available by pressing ) where you should notice things such as the glowing area (your location), the M (Map Station), the S (Save Station), your ship (also has an S for Save Station), the locations of other regions (Brinstar, Wrecked Ship, Maridia), and the areas of the map with a dot within them (items of interest/upgrades).
Head out to the left, kill the enemies and head through the door.
Continue up, head through the blue door on the left that you have to roll to get to. This is a Save Station, enter it to be asked whether you want to save or not. Select Yes and press to save your game.
Morph Ball Bombs
Head out and continue to the top area. Move to the right, taunt the drill bats to dive or shoot them, continue to the right and roll down into the hole within the mound. You cannot return back up at this moment (the exit is blocked by morph ball bomb breakable blocks). Head to the bottom and through the blue door to the right. Make your way right killing all the flies from far away (a swarm can be nasty). Continue through the pink door.
It's chozo time. Blast the orb, jump and grab the Morph Ball Bomb upgrade, press start to make the instructions disappear. Notice that the door closes and is gray, you're locked in!
An Unexpected Foe
Run to the left corner and wait there. The chozo's armor begins to crack, and fall away, before it awakens. Begin attacking after it stands up and gets close to you, its stomach will begin glowing so switch to missiles and unload on its weak point (its stomach), switch back and just keep attacking until its stomach explodes (25 shots or 5 missiles). The chozo will follow a pattern in which it walks forward, stops, continues until it hits you, claws at you, jumps back, fires explosive orbs from its mouth and then repeats (although it might fire arc beams at you if you duck). Just attack it at all times, avoid the explosive orbs by either getting close, jumping over them from left to right, or wall jump off the left wall.
Eventually the stomach area will explode, you know you're making progress now. It will begin dripping spit like fluids at all time from it (aesthetic effect), just continue fighting. Its head will explode after 10 shots (if you can get a missile power up from destroying the orbs, you can waste him with just two missiles), you're getting close, just avoid getting hit. He no longer can shoot orbs so he will only patrol back and forth trying to claw at you. If you get close, he'll swipe with his arm, but you can use this to your advantage by running close, moving away then firing so that you have more time. The best strategy though is to move to one side, fire, when he gets close jump up over his head (preferably a wall jump to avoid damage) and then run to the other side and repeat until dead. He will explode after four shots (1 missile). This can be known as the mini-boss of Crateria although Crateria doesn't have a boss.
Your journey continues in Brinstar.