By exploring abandoned bunkers in ATOM RPG, your character can get exposed to radiation. This page of our guide to ATOM RPG contains information on the negative effects of radiation. It can weaken or even kill your character.
The easiest way to remove radiation is to buy alcohol. Almost every town has a merchant selling alcohol. You need vodka, moonshine or Ukrainian gorilka. Beer won't help you here.
Ostradnoye, the first town in the game, has a doctor. You can find this NPC in the building presented in the picture above.
To heal your character at a doctor, ask this NPC for help (the first dialog line). The doctor will examine and heal you - all for free.
You can come across an antidote that removes radiation from your body. Drink it to help your character.