To edit a video clip in a timeline, import the clip, drag it to the timeline, then highlight the section you want to dissolve and drag it to a new location. To add a smooth transition, go to video transitions and select cross dissolve. This will correctly place the effect between the two sections. Other editing options include cropping using the razor tool and deleting segments using the arrow selector and delete button. When finished, export the final clip using the export to QuickTime option.