The doctor Is meant to heal your team and avoid dying to keep on healing and build ubercharge, In order to heal you need to press 2 on your keyboard and click and hold on a target. Ubercharge breaks stalemates so it is very powerful. You can give your pocket ( person you are healing ) and you 8 seconds of invincibility, 8 seconds of critical hits, or increase your healing by 300%.You need to fill up a bar in order to get this ubercharge and it's lost on death so make sure you avoid the other team and heal your team. NEVER HEAL ONE PERSON, you should heal everyone to be more effective and you build ubercharge MUCH faster if you heal everyone. medic is THE HARDEST class to master so make sure you don't give up if it's too hard I recommend watching "arrayseven" and learning from him. links are right here below
https://www.youtube.com/watch?v=vHntb0kp2K0 This is for new players
https://www.youtube.com/watch?v=eQbS1Oir58o&t=37s this is for medics who want to spice up there game
https://www.youtube.com/watch?v=w6SwwnKnnR0&t=678s All medics should watch these
https://www.youtube.com/watch?v=9APIMD0WgXg all medics should watch this
https://www.youtube.com/watch?v=JkjShJGh_lU all medics should watch this
