1) Login as admin/admin.
2) Click on the Admin tab in the navigation bar
3) In the Manegement Portal, click on "root" on the left-hand side (root is a collapsed tree view)
4) Enter the Portal Name and click Add portal
Now, when you expand root, there will be two portal, default and the one you just now created.
To add pages, click on the new portal in the tree view and create pages using the Add Page button. Use similar steps to add portlet instances to the pages. The documentation provide very good instructions for creating pages and adding portlets, read it.