The same way you originally do it. Download WordPress. Unzip. Place on server. Create a database, edit the wp-config-sample.php file and save it as wp-config.php. And then point your browser at the server and it should take you through the 5-minute install. See http://codex.wordpress.org/Installing_WordPress
WordPress can also be installed through the backups. There are various methods to create backups. You can use plugins for creating the database backups or full site backups. You can also create manual backups. Restoring WordPress from those backups files is dependent on how you created them. For example, if you have created the backups using the ‘BakupBuddy’ plugin, then they can be restored by using the same plugin. Manual backups need to be manually restored.
What do I do to create a database? The first time I did this I used the iPage.com link. I didn’t use an ftp the first time.
You can also follow the iPage user guide for WordPress installation http://www.ipage.com/knowledgebase/beta/article.bml?ArticleID=1750
