Can't start discussion

Please tell me how to do this?)

I would guess the user trying to start the discussion hasn't verified their email address yet.

I want to do the same on the site. Now I have "only admin" permissions, but other users can add a post there, simply through moderation

I don't understand the question. Are you trying to give permission to post, or remove permission to post? What are your current permission settings?

I see what he means...he want's to limit the button on certain tags.

In the permission grid we have solved set to "create discussion" "admins and mods" or something similar, that blocks users from selecting the tag.