What do you mean? If you are talking about closing a thread, then you can't do it by yourself. If the question has already been answered and to avoid some off-topic/rant that may follow after, then usually a moderator comes and closes the case
i don't know how to end a discussion. Does anyone know it?
The short answer is you don't: you may start a discussion, but discussions continue until no one else wants to continue them (or the mods close them for violating a forum rule, and I don't recommend attempting to close a discussion in that way).
Comments
If you are talking about closing a thread, then you can't do it by yourself. If the question has already been answered and to avoid some off-topic/rant that may follow after, then usually a moderator comes and closes the case
If you mean closing, then only mods can close