Timeline is a temporal scale, corresponding to the time of the result video. The cursor of the timeline points to the frame in the result video. In its own turn, the preview window reflects the frame pointed by the cursor. Besides, you can change the sizes of the timeline, pressing the buttons 1&2, but the button number 3 returns the timeline to the initial size.
Timeline is responsible for video editing. By means of the timeline you can point and then delete some parts of the file from the result video. For this action you need to show the initial position of deletion (just click in a needed place) and, holding the button of the mouse, show the final position. After that you can delete the detailed area by the button "Delete" or "Add area of deleting".
All the actions can be cancelled. To do this, you have to choose the part you want to restore and press the button "Remove Area of Deleting".