Projects in BlockNote.Net
In BlockNote's case, projects are folders on your hard drive where you store your html files and images. These folders are just display the content of the corresponding directories on your web server.

To open such project-folder just click on "Open folder..." hyperlink at the top of the Project folders panel an select the desired folder.

To open an html file for editing "double click" on it in the Project Tree. If you double click on picture file, BlockNote will open your default image editor with the picture loaded.

You can attach a project pane to the right or left side of BlockNote's main window by clicking on the arrow button at the top of the Project folders panel.
When you don't need the Project folders panel at all, you can switch it off by unselecting Project Bar in the View menu.