Brinstar
After Samus awakens, head to the left. Jump up and over the outcropping. Touch the red orb on top of the rock to obtain the Morph Ball. Return back the way you came; since you cannot jump over the outcropping, you must go under it. Activate the Morph Ball and roll under it. Continue heading right, past where you started, until you reach a door. Shoot it to open it. In the next room, note that the top platform can be destroyed by shooting it. (You'll have to wait until you get a later item until you can destroy the cracked floor.) Continue to the right.
In this room, if you check your minimap (or press Start and view the full map) you'll find a small white circle. This circle indicates that there is an item (such as an Energy Tank) in this room. The map circles are always accurate, even if looking around the room suggests otherwise; more often than not, the items are hidden. This particular item is hidden in the ceiling, where you cannot get to it. (You must shoot the ceiling to expose it, and then jump up and grab it; unfortunately, at this point in the game neither your beam nor your jump cam reach to the ceiling.) Enter Morph Ball mode again and roll under the wall. The room seems to dead-end with a stone statue of an alien with a outstretched, glowing hand. This is your first Chozo statue. Position yourself so you're standing on the statue's hand, then enter Morph Ball form. The full map will appear, with a glowing dot indicating your next target. Press A to exit the full map; the statue will then "sit down" and reveal a path behind it. You will then be healed to full strength. Continue through the door to the right. You have now entered the room I will refer to as the West Shaft. (If you continue to the right, through the blue door opposite the one you entered through, you will find a Save Room. Save Rooms are marked with a yellow S on your map.)
Use the platforms to ascend through the West Shaft. You'll see your first ripper enemy about three screens up. I make a note of this as rippers make excellent platforms once you can freeze them with the Ice Beam. (There is another enemy you'll see later, the ripper II, which is a faster version of the ripper.) For now, just avoid touching it and continue upward.
About seven screens into the Shaft, you will see a Morph Ball tunnel leading to a door. This tunnel is blocked, but you can destroy the plug with your beam — well, most of it, anyway; your current beam cannot destroy the entire plug, as it cannot reach to the very end. (15% walkthrough- Stand above where the blockage ends, hold L and press down, then fire to reveal a secret passage) Continue up. Two screens above the plug I just described, you will find a door leading to the left. Take it. (If you continue up from there, to the very top of the Shaft, you will find another door, but if you take it you'll find yourself on the wrong side of a Chozo statue. Since Chozo statues can only be interacted with from the side with the outstretched hand, you cannot proceed in this direction.)
Continue to the left, using your Morph Ball and beam as necessary, until you reach a door. Inside is the first Chozo Gift Statue you will meet. Shoot the ball in the statue's hand, then touch the item within. This Gift Statue gives you the Long Beam. After you pick it up, the Gift Statue's hand will glow blue; touch it in Morph Ball form and you will be fully healed. Exit through the door. Since you cannot return the way you came, take the upper tunnel instead. Use your beam to destroy the plug, then roll through the shaft. At the end of the shaft, jump up and you will enter a secret room. Secret rooms do not appear on the map until after you have entered them for the first time; once you have entered them, they will be coloured green instead of blue. Follow the path up and to the left.
Once you re-emerge into a room already on the map, you will see your first pools of acid. Acid looks like orange fluid, and will damage you constantly if you fall in. What's worse, you move much more slowly when even partially immersed in acid. Head to the left. The next room is a dead-end, but I have lead you here for a reason: This room leads to Tourian, where Mother Brain dwells, but your path is blocked by a strange gate fashioned in the shape of two alien heads. This gate will only open when you have defeated both Kraid and Ridley (the aliens whose heads grace the gate). Since there is nothing more to do here, head back to the right. Once you reach the door, a sidehopper will drop through the ceiling and attack you. This enemy can take more shots before dying, but is no more dangerous than any other enemy you've met. Kill it, then head through the door on the right.
This room contains a Chozo statue. Enter its hand in Morph Ball form. Once you know where you're going next, press A. The statue will sit, heal you, and then you are free to go. Head to the right. You will now be at the very top of the Shaft. Drop down until you reach the plugged tunnel you saw when you were here earlier. Now that you have the Long Beam, you can destroy the plug in its entirety. The door leads into a small connecting tunnel that leads into East Brinstar, an area that is not initially on your in-game map.
When you cross into East Brinstar (Into the room that I will refer to as the Central Shaft) you'll notice 2 thing: 1. The Colour of the rock has changed from a Blue-Grey colour to a brown colour and 2. on the other side of the central shaft is a red door. No beam attacks can open this door- you'll need to find some missiles. Head down the shaft. The first blue door is a save room, the second leads to missiles. A small purple bug called a brug will try to latch onto you, ignore it, you can't hurt it and, on it's own, it can't hurt you. Go through the 2nd blue door and you'll find that the room is shaking. Run across the room and jump across the pillars over the acid pit to pick up the missile tank, then go back to the entrance. (Don't go right (>) yet- the path to Norfair is blocked by bomb blocks) Before you reach the door though, you will be ambushed by Deorum. Refer to the boss section to kill this king of worms, or wait until he gets bored and...moves away. (Of course, no-ones actually created the boss section yet so i'll just say here-Deorum (Japanese for King worm) is a giant, one-eyed, spiked worm who uses the charge beam's charging effect to smash his head into you and eat you. Shoot his eye with missiles when it's open and shoot the spikes he shoots at you to recover ammunition. It only takes 3 missiles to kill the worm who would be king, but miss and he'll run away.)