The Medic station is a building that can be built by the Allies (Upgrade the Bunker to Aid Station for the Wehrmacht.) The medic stations deploy medics and bring back heavily wounded soldiers for standard medical procedures, if 6 wounded soldiers for the US, 4 wounded for the Wehrmacht or 5 wounded for the British are brought back to a medic post, doesn't matter which one on the battlefield, you get a free squad.
If you're the American Army you get a six-man Riflemen Squad and the Triage center automatically heals your teams' wounded men. If you're the Wehrmacht you´ll get a four-man Grenadier Squad, all Wehrmacht units are also equipped with Field Medic Kits that can be used infinitely in your territory, as long as you have munitions to pay for the cost of 35 munitions. If you're the British Commonwealth, you'll get a five-man Infantry Section but the British Medic Station requires Munitions to heal for a limited time. However for the Panzer Elite, you have to "buy" the function to heal your teams' units at your HQ and Reinforce Point (the Panzer Elite equalient to front HQ, which can't build anything, just reinforce and heal). The HQ's heal radius is just outside your base's Command Territory.
The radius of a medic station is relatively limited (although it´s still quite big), so your medics won't run too far just to pick up a wounded soldier. The medics will also not pick up torn-apart soldiers, those who died horribly by massive artillery strikes for example.
The Medic Bunker of the Wehrmacht has some advantages against the Allies facility: You can garrison Infantry units like MG-Squads inside the Bunker and produce goliaths, abilities the Allies lack.
The Soviets doesn't have any of these installations, instead, they have a mobile medic truck, that has to be locked down to heal nearby friendly units.
A good idea is of course to have medic stations somewhat spread out, preferably near the frontline but out of harm's way. If you can afford it, have also one in your base, so that if all medic stations on the field gets destroyed, this one still holds the remaining wounded soldiers.