Initially, it is impossible to add files from the Media Bay or record new material to the installed Sequel demo and tutorial. The audio tracks cannot be record enabled and when trying to drag and drop files into the project nothing happens.
The default settings do not allow modifying the existing projects. Therefore, those projects are write protected and Sequel loads them using the path "demos and tutorials".
All projects you want to add new media to need to be copied into another folder. A new project location has to be defined in the program settings page and the Sequel demo and tutorial projects of your choice have to be moved from the Sequel application folder into that new folder. You can of course use an already defined folder as well.
If you reload the projects from that new folder, you can record enable the tracks (please make sure that a defined input from your audio card is selected on those tracks!) and you can add new material from the media bay or from other locations by dragging and dropping them into the project.
If you have created a new project, the above procedure is not relevant.