You have a SharePoint Server 2013 Service Pack 1 (SP1) Web application that has the
URL http://portal. contoso.com. You have a site collection that has a top-level site named
http://portal.contoso.com. The site collection administrator deletes http://portal.contoso.
com. You need to restore only the http://portal.contoso.com site collection from the last
backup of the farm. What should you do first?

A.
Restore the hosting Web application to the current Web application location.

B.
Run stsadm.exe and specify the -export option.

C.
Restore the hosting content database to a new location.

D.
Run the restore-spsite cmdlet.

Explanation:
To do site restores the syntax is almost just as easy. You will need to use the same SharePoint 2013
Management Shell as doing the backup.
Restore-SPSite-Identity SiteCollectionURLHere -Path BackupFilePathHere [-DatabaseServer
DatabaseServerNameHere] [-DatabaseName ContentDatabaseNameHere] [-HostHeader HostHeaderHere] [-Force] [-GradualDelete] [-Verbose]
DatabaseServer Specify the server for the contentdatabase
DatabaseName Specify the name of the content database
HostHeader URL of the Web application that will hold the host-named site collection
Force Overwrite the site collection if it exists
GradualDelete Recommended for site collections over 1 Gig in size, existing data is marked as deleted and
gradually removed over time by a job rather than all at once to reduce the performance hit of deletinglarge
amounts of data
http://www.bradleyschacht.com/backup-and-restore-sharepoint-2013-site-collection-with-powershell/