Halo: Combat Evolved/The Pillar of Autumn
You, Master Chief, have been preserved in the Cryo-Tube. An engineer of the ship will deactivate the Cryo-Tube and perform a couple of diagnostics.
Once you exit the Cryo-Tube, an engineer will conduct some basic tests to ensure your controls are configured as you like them and their accuracy. He will also enable and test your shield. Once he is done, he will tell you that Captain Keyes expects to see you at The Bridge—The Pillar of Autumn's cockpit.
Follow him. He will die in a freak explosion in his attempt to guide you to the cockpit, so now you'll have to get there yourself.
Go through the passage. You'll fine the door jammed, so to the left of you there is a large tube, jump over it. Continue down the hallway, walk through a door, and crouch under the next jammed boarding door.
Take a right and continue walking down the hallway until a closing boarding door prevents you from continuing. To the left of it is a small door. Walk through it.
Uh oh, covenant! Run past the covenant and continue along the path. Once you are at an intersection with a hallway, there should be a man in armor. He will help you get to the Bridge from this point. Follow him.
Once you arrive at the Bridge, Captain Keyes will be waiting for you at the very front of the cockpit. Approach him to trigger a cut scene.
 Al Constructs and Cyborgs First!
Captain Keyes has decided to abandon the Pillar of Autumn, and he's giving you the responsibility to take and protect Cortana, a computer program holding vast amounts of information about humanity. Time to get off the ship!
Keyes will hand you a pistol, but it is empty and cannot be used until you get ammo for it.
Glitch: It is possible to hold three different weapons at once! Check the sidebar for more information on this.
Get out of the cockpit the same way you came in. At some point, Master Chief will pick up precious pistol ammo (to pick up ammo, simply walk over it.) After the next door there will be three covenant. Take them out with your now-obtained pistol and enter the next closest door.
Now you will pick up an Assault Rifle (also just by walking over it.) Take out a couple covenant with it and enter the next unlocked door at the rightmost corner of the room. There will be more covenant, use your Assault Rifle to take them out. When you kill a covenant, pick up their weapon. It seems that Covenant weapons deal more damage than the human weapons you currently have. Be sure to replace your weapon every once in a while, as the Covenant weapons run on batteries and they cannot be reloaded.
There will be a door similar to the one you used to enter the Bridge. Walk through it and continue down the path. There will be an Elite along the way, take him out. Pass the next boarding door.
The Airlock was used by the Covenant to enter the ship! Take out the covenant and enter an airlock to take a shield. Go back out and enter the next maintenance door, where you will hear soldiers and covenant in battle. To your right should be a path with a grunt running through. Take him out and his accompanying covenant.
Enter the next maintenance door to take out even more Grunts and look for an open Airlock. Along the way there should be a fork in the path, continue walking forward. Be sure to reload. A forced right will take you to more Covenant, take them out and continue walking down the path.
The next airlock was also invaded by covenant, take them out. In the event the shield you picked up earlier has worn out (if your health meter no longer shows a greenish bar), take more shield from the covenant craft. Your shield must be completely worn out before you can pick up a new one.
Continue down the path. Once you reach a hallway, take another right to branch into a smaller path and take out more Covenant. The weapon of choice here is the Covenant Plasma Rifle. Continue along the path.
Finally, you will see stairs. Quickly take them, and kill more Covenant on this floor. Take the next open boarding door and continue down the hallway to kill more Covenant.
Continue down the hallway until you reach three more abandoned airlocks. Continue down the path and take a left to open another maintenance door. Cortana was kind enough to show you where the door was with a Nav-point.
Once you're in, you might want to use your flashlight. Like any other function, on your screen you'll be shown which button to press to toggle your flashlight.
Forking about 5 meters off the path, take the path to your left and continue down it until you reach another fork. Then, go on the path to your right until you reach the next open maintenance door.
Walk through it and continue until you reach a busted maintenance door. Cortana recommends you Melee it. On-screen help will appear to tell you which button melees. Hit the door with a melee and continue.
There will be a grunt along the path, with his back turned. Melee him on his back, causing an instant kill. An Elite will be blocking a door, also with his back turned. Melee him on the back.
More covenant will be waiting for you. Take them out with your Plasma Rifle (or Assault Rifle if you don't have a Plasma Rifle) and walk through the next open maintenance door at the end of the hallway. Take out a grunt and pass through the next open door. Look familiar?
Continue down the path until you reach a hallway with more covenant. Take them out and go through the busted maintenance door to the left of the barricade. It's dark in the path, so turn on your flashlight to make the way more visible. En route there will be two covenants, so be prepared to take them out.
Finally, pass through the next unlocked maintenance door and kill the covenant with your rifle. Continue walking through the hallway as you kill more covenant until you reach the last three airlocks. Walk into the middle one to trigger a cut-scene once you've taken out most of the covenant.
Congratulations, you have beaten the first level of Halo! (Now try it on Legendary...)