To create a project, you need to be in the Roadmap tab of a project portfolio card.
To create your project, simply click on the blue "+"button at the top of your view, between the side panel of your pinned views and the display level icon.
This will open a pop-up window allowing you to choose whether you wish to create an empty project, or from a template (this is possible if you have defined project portfolios or projects as AsTemplate).
Your project will then appear as a child in your project portfolio.
Alternatively, right-click on the project portfolio line and select the "Add project" option.
Then repeat the operation on the project lines etc. to create a project treeproject portfolio -> Project -> workpackage -> Action ->Task).
