You can use both sites, either by giving out the link to the customer or you can include the pages with an iFrame into your own website.
You can enter the hosted signup page at "Products > Plans > Plan variants" by clicking the hand-button or by pressing "Show signup page" at the bottom of the the settings of a Plan Variant.
You will be redirected to the wanted signup page, which can be customized and looks like this:
You can customize the colors of the page, add your corporate logo and select which fields shall be shown and are mandatory or optional. If you want to display this page in different languages, you have to save the descriptions in the wanted language. By adding the suffix ?language=en / ?language=de / or ?language=fr you can show an englisch, a german or a french signup page. You can find all the necessary options in "Settings > Integration > Self-Service".
You can find the hosted customer portal by going to "Customers > Contract Id > Perform Action > Create Self-Service Token" and clicking the link.
In this customer portal, the customer can change his invoice and payment data, see his current subsription, his balance, cancel his subsription and download his invoices and credit notes.