In order for ProvisionPoint to create Site Collections for you, it needs to have a Managed Path location to create them under. You can decide that on the 'Managed Paths' page.
Add a Managed Path
Navigate to the 'Managed Paths' page, under Resources:
Here you'll see a list of your Web Applications (added through the Web Applications page, under Resources). You can now enter the Managed Paths you'd like ProvisionPoint to know about. Simply select an appropriate Web Application from the dropdown, and enter the managed path you'd like to create sites under.
You can now link these Managed Paths with Service Definitions - see Decide Where a Service Definition will Create Sites.
ProvisionPoint will not be able to actually create managed paths for you in your SharePoint environment. You'll need to do that yourself (if you're using anything other than /sites/). This page simply allows you to tell ProvisionPoint about all the managed paths you already have.