Remote coding is the process of getting a remote control to send the code that the receiver of an automatic door recognises. Without that code, the remote works but the door takes no notice of it.
How it is done depends on the remote. On old ones, the code was set with small switches inside the remote, which had to be put in the same position as those on the receiver. On current fixed code remotes, the signal is copied from the remote that already works. On rolling code remotes, on the other hand, the usual thing is to register the new remote on the receiver, and that step is done by whoever has access to it or the person the community appoints.
So before buying a remote, it is worth knowing what type yours is. From a photo we identify it and tell you what is needed: you will find it in garage remote duplication.