You have to Create a Site Collection in your Web Application. Go to Central Administration and choose Create Site Collection in the Application Management group.
Enter a title in your Site Collection, select template to use and the primary site collection administrator:
This can be done using PowerShell as well. Don't forget to Set Execution Policy and add PSSnapin for Microsoft.SharePoint.PowerShell. First find out which template you're going to use through this command:
Then assign the chosen template to the template variable:
>$template = Get-SPWebTemplate "STS#0"
Finally create the site collection:
>New-SPSite -Url "<URL for the new site collection>" -OwnerAlias "<domain\user>" -Template $template
Reference Create a site collection in SharePoint 2013