The Megaton clinic is Megaton's local clinic. Doc Church is the only doctor in Megaton.
Doc Church is the physician in charge, you can purchase medical supplies, heal your wounds or get rid of your rads. There is a holotape about the Replicated Man on his desk in the back (which you can talk to the Doc about), and the clinic medical supplies (only accessible if you kill Doc and steal the key). There is a room opposite the entrance which may be empty or housing up to three unconscious patients.
There is a holotape on top of Doc Church's desk to the left of the broken computer terminal entitled Wanted: Trustworthy Surgeon. This holotape can activate The Replicated Man quest.