Adding reply feature in my forum project?

I want to add reply feature on the post in my forum project, but I don’t know how do I add reply feature in post, any help?

do you mean the one that you take data from this forum?
in that case take a look at the discourse API: https://docs.discourse.org/

I don’t think you can, as it seems more an admin feature

If you are talking about your own project,
you should give us some details about it.
You probably use a server and database, don’t you?