The aim of the game is to help Doctor Winston cure the patient, who has been infected by many dangerous viruses. You can do that by using different medicine provided you by the Doctor.
To exterminate a virus you have to place at least three pills next to it.
It doesn't matter where you put them. It can be above, beyond or next to the virus.
A context menu should be shown when right-clicking or, on touch devices, long-pressing in the game. This menu especially allows to play in full screen and control the volume.