It is about copying the files from your backup to the folder of your WordPress installation via a FTP client like FileZilla.
Restore WordPress With Backup By BackWPup Via FileZilla
Here is a tutorial on how to restore your problem WordPress site back to normal.
1. Firstly install a fresh WordPress to the domain you are restoring. Go to http://wordpress.org/download/.
You can learn how to install WordPress from here.
2. Then install BackWPup plugin.
3. Copy the backup file (zip file) from Dropbox to your desktop
4. Now you need to copy the zipped file from your desktop to the PUBLIC_HTML folder of your domain with Filezilla.
5. When you open your FileZilla, you can see the backup file under the "Filename" on the left side.
6. Click on the file and drag it across to the domain which is on the right side under "Filename".
7. Now look for the database file (SQL file) in the zipped backup file. The name is something ends with .sql
8. Extract this SQL file from your zipped backup file to your desktop. Click and drag it to the desktop.
9. Go back to FileZilla and refresh it. You should see the database SQL file on the desktop listed under Filename on the left side.
10. Now copy or drag it over to the right side of the page copy that file to the public_html folder.
11. Go to WordPress dashboard. Look for BackWPup under Plugins.
12. Click on Tools. You can see the SQL file stored inside public_HTML file appears above the Restore button.
It looks something like this: SQL File to restore: /home/ xxxxx/public_html/xxxx_wrdp1.sql
13. Now click Restore button.
14. Next go back to FileZilla to delete the SQL file from the public_html folder on the right side of the page.
15. Now log in to your web host site (Bluehost, HostGator, etc). Open up cpanel, click File Manager, and select Web Root (public_html/www).
16. Now you can see the zipped file there.
17. Find your zipped file and click on it. Then click on Extract which is on top of the page.
18. A box pops up. Click on Extract File(s) button.
19. Click Close button below.
20. Now go your site and check it out. If you have opened earlier. then you have to refresh it.
21. Your site should have restored it perfectly.