That this mission can be a little tricky for those who want to earn the achievements/trophies for completing the game without killing any human enemies. The first part of the mission has us in a cart in a shoot-out with enemy soldiers riding on an adjacent track. If you wish to do this without killing anyone, use the crouch button to hide behind the fortifications on the vehicle as best you can and use your medkits when you get hit a few times. Essentially you can keep this up until Artyom jumps across to the train to begin the next stage of the mission.
Note: There is an achievement for killing all of the enemies before jumping onto the train. However due to this walkthrough being written from a stealth/ no kills point of view I would recommend going the no-kill run route first and loading this chapter from the main menu once you have completed the game to do your killing!
Once you are aboard the train, the enemies guarding it will be aware of your presence and shoot at you. To get through here without killing them you will need to stay in cover and wait for a break in the shooting to sprint up to the nearest enemy, crouch and use the takedown button when the prompt pops up. Loot the body (you’ll be in dire need of those medkits !) Re-enter cover and repeat this 4 more times until you reach the first cabin.
As soon as you enter, grab the Diary Note [Note 1/1] from the top of the blue crate just in front of the door. Work your way through the train car here and take out the next 7 guys in the same way as we did previously. This can be really tough to do without killing them. Just remember that if you take too much damage, you can back off a little and hang out in cover until you recover a little before continuing. Also be sure to loot the unconscious bodies for medkits as you go.
Continue through the next carriage until a scene plays to end the mission.