You can double-click a file to display it in the designer, tool or editor associated with the file type.
Right-clicking a folder will provide you with a context menu from where e.g. new folders or files can be added.
Right-clicking a file will provide you with a context menu from where e.g. the file can be removed from or added to the project. You can also choose to enable the file for display in Project Map or edit the properties (see Folder/File Properties (p. 85)).