As the description suggests this achievement is divided into three "short" parts. This achievement is missable but it is unlocked very early on in the game and you only have to replay about two chapters if you select EXHIBITION from the chapter select.
1. On the level EXHIBITION you will eventually arrive to a market area. There is a man sitting on a bench and when you approach him he will tell you that his child is sick and that he needs some bullets(currency) to buy medicine. Give him the bullets. (If you can't find the man, he is in the first big hall area. If you arrive at the armory where you get your equipment then you have gone too far).
2. Continue the game normally(don't quit out) until you get to the RIGA level (two chapters after EXHIBITION). After the intro scene where you are in a bar celebrating your recent affaires you will stand up from your chair and regain control of your character. Walk down the stairs and head right. You will enter a cutscene with a child about a man who wants to see you. The child will guide you to him for a bullet. Give this bullet to him. You don't have to follow him after giving him said bullet.
3. Now turn around from the child and run to the other side of the room where the train platform is. You will notice a beggar on the ground and if you stand close to him you are able to press the action button/key. Do this for your final objective and the achievement is yours.