@ludam you can set the minimum & maximum tags for a post in ACP -> Settings -> Tags page. I don't think there is any option to set which tags a user would be able to use.
shall admin prevent users to add new tags in nodebb?
I'm a novice develpoer, and I DO NOT WANT MY USERS TO ADD NEW TAGS. How can I do for it. Or can I delete some tags?
Search "tags" in the ACP search bar. There should be an option to manage tags and only allow certain ones.
@PitaJ is correct, the option is called the "tags whitelist", and you can decide which tags to allow, and do so on a per-category basis