This is a quick example of how to restore an example directory: /var/www on your server.
Step 1
Create a file backup for /var/www (as an example).
Step 2
Go to your backup page, under the "Backup History" section click the little "i" on the right, then click "Raw Download Link" and copy the output.
Step 3
On your server, run the following command, replace the raw download link you obtained in the previous step:
wget "PasteTheRawDownloadLinkHereBetweenTheQuotes" -O "backup.tar.gz"Step 4
Now that you downloaded the backup on your server, restore it as shown below by running:
tar --overwrite -xvf backup.tar.gz --directory / var/www
Note: this will overwrite your /var/www directory by the one in the backup archive. It is a good practice to extract the backup in a temp folder first and inspect it.
If you need any help in any of these steps, let us know and we can help you with the restore.