Ok need to know how to backup it all Mybb in case for hacking or some server error and how after that reverse all my post, thread and users..
wich mean if install new fresh Mybb how to add files from backup with post,users and thread,,Any Tutorial??
You can take backups via the ACP (ACP -> Tools and Maintenance -> Database Backups), or through your control panel (or phpMyAdmin).
To restore a backup, you just import the backup to a database.
More detailed instructions
here.
do i need both backup from admin panel and backup from phpmyadmin or just one??
also how to add in fresh install only database with users,posts and thread??
No, you need just a backup from the admin panel.
IMPORTANT: You backup the DATABASE, not the files of your forum.
If you want the files, you have to do that from the cPanel