On the Main page, you will set the Domain(s) that the store will use, and also set the Document Root.
You can select different sites in the left-hand column, and access various configurations in the top tabs.
When making changes to any page, you must click Update to save, or can hit Cancel to revert changes.
Domain(s) to Listen On
Set the domains that the store will use, separated by a space. You will need to add both domain.com and www.domain.com in this field.
This is the path that your Magento 2 store will run from, and is relative to the /srv/ path. In the above example, the full path is /srv/m2. Click the Directory icon to the right to select or create different Document Roots.