All your iMovie video projects are listed in your Project Library, where you can preview them and open the one you want to work on.
To preview and open a project:
Do one of the following to preview the project:
Click to select it in the Project Library, and then move the pointer over the filmstrip, to the right of the project’s name, to skim the project.
To play the project from the playhead (the red vertical line), press the Space bar; press it again to stop playing the project.
To open a project to work on, double-click it in the Project Library, or select it and then click the Edit Project button in the upper-left corner of the Project Library.