Unexpectedly, you found a young boy named Kirill in the underground. The boy has agreed to help you and wants to take you to his hideout, as described in the following chapter of the Metro Exodus tutorial.
Follow Miller and Kirill. After a short time, you will again be attacked by mutants and it will be necessary to kill them. Deal with the threat, and then wait until Kirill appears again. Follow the boy to his hideout.
Ask the boy about his father and the situation in the city. You will find out some interesting things and you will decide to split up. Make sure you take the powerful railgun from the room and use the workshop to replenish all your supplies. The final stages of the game are around the corner, and you have to prepare yourself well.
When you're ready, crawl through the manhole and go outside. Your task is to recover medicine for Anna, which will not be easy, because you have to reach the deepest parts of the metro. Walk forward, then through the wagon, jump on the other side and fight the mutants.
When you're finished, go upstairs and continue, walking the old scaffoldings. At this point in the game, the compass arrow, which points the way, will be invaluable. After some time, you will reach a very bright room, which will quickly become overgrown with mutants. Fight the enemies, then turn the knob that's next to you and proceed.