I am lookin to do this just as small project.

How would I actually implement some type of server or something to constantly be listening for a webhook? I have very limited experience with servers. At a very high level, how would I do this? For context of the type of answer I am looking for, the only way I can think of is to a program constantlyrunning on the pi. But is there anyway just to run a script if the pi detects that something is trying to post?

Thank you!