In Immune, you first choose one out of 16 viruses to play against: there are easy, medium and difficult ones. Each round consists of 3 phases: viral replication, energy allocation, and immune actions.
In the viral replication phase, you will place virus tokens on the body organs (this may cause debilitating disease symptoms). In the energy allocation phase, you move energy tokens on the action tiles to strengthen their effectiveness. Then, in the immune actions phase, you perform two out of nine available actions as shown on the action tiles. You win the game if you manage to defeat the virus and remove its strain from the board.