This really depends upon your hosting solution.

If you have CPanel:

To restore your MySQL database you would log in to CPanel.

After accessing CPanel, you should select the MySQL maintenance icon. Usually in this area, there is a link to phpMyAdmin or other MySQL management tool.

Working under the assumption that you are using phpMyAdmin, select the appropriate database for your website (or create a new empty database with the same name if it was deleted).

Select the SQL tab along the horizontal navigation bar. This will then allow you to either paste in the SQL dump script or browse your computer for the location of the SQL backup dump. After selecting the appropriate file, or pasting the appropriate script, select the GO option to execute. Any errors from the load will be displayed to you. You will want to make sure that the database is empty or that the tables have been cleared down to avoid data integrity issues.

To restore your Xoops files, simply log on to your website root directory via FTP and copy/overwrite any existing files with your backup files. You may want to clear any pre-existing Xoops files in the root folder to make sure it is a "clean" restore.