A Medic simply heals your units when not under attack and it is quite weak so it is advisable to keep it out of battle. Medics resemble Repairmen the difference being that the hat of a Medic is red as opposed to the Repairmans blue hat.
Medics are the most expensive foot soldier to be spawned from a Barracks costing $145.
The Main funtion of a Medic is to heal your soldiers. they are extremely weak so keep them out of harms way and garrison them within a bunker.