As a first step, to create a movie project choose 'File' > 'New Project ...' and give the project a filename. Then you can import source clips, i.e. video, audio and still image files, by dragging them from the Finder to the 'Browser' window. Alternatively choose 'File' > 'Import ...' and select the desired files (while holding down the command key). Double-clicking a list item in the 'Browser' window will load the media clips in the 'Monitor'.
Now, in order to prepare a clip for the insertion in the movie project's timeline, set the in and out points. For this purpose hit the corresponding buttons in the lower right-hand corner of the 'Monitor' window. If you have already selected in and out point, you can go back to these points in time holding down the shift key and pressing the in or out point button. Next, select a track in which you intend to insert the clip and then press the 'Insert' button. Note that all subsequent clips will be relocated. One can modify the insert command to an add command by holding down the shift key. This way subsequent clips won't be moved.
Thus far we have worked in 'Editing Mode', i.e. the 'Monitor' displayed a single clip. Notice the gray 'P' button in the 'Monitor' window. Press the 'P' button (it will become blue) to switch to 'Preview Mode' in which the 'Monitor' shows the whole movie project's composition. Alternatively you can drag the playhead slider in the 'Timeline' window to change the mode. Whenever you double-click a clip, which is already in the timeline, the clip (if it is not a title clip or a screen movie clip) will be loaded into the 'Monitor' (the 'P' button becomes gray indicating that we implicitly switched to 'Editing Mode'). By this means one can re-set the in and out points. Whenever you single-click a clip in the timeline, the clip's properties will be shown in the 'Inspector'. It allows you to do keyframe animation among others and change all the clip settings.
Please read the user's guide carefully to get a deeper understanding of all the powerful tools that the FastCut video editor provides.