From your side, you can customise the look and feel of a user’s account by setting the company logo, changing the colour scheme and providing a splash image that is displayed to the user on the homepage when they login (maybe an image to promote specific products or even just a secondary logo).
User accounts are created and associated with your customers in Dynamics 365, where you can easily manage their account permissions including functions such as disabling or resetting passwords. You are in control of the menu structure on the portal and you define the catalogue and prices to show for a customer.
With the Extranet being in real-time with Dynamics 365, any changes you make are instantly shared with your customer base. It even supports multi-language, allowing the user to easily switch between their preferred language!