When and How to Add Transitions to your Videos
If you are adding images to your video or would like a smoother cut from scene to scene, you'll want to add a transition to your movie.
To preview any transition, double click the thumbnail, and it will play in the window on the right. When you have found a transition you would like to use, drag and drop it into the timeline between two clips where you want a transition. Once it's there, you can see what the transition will look like in your video.
If you don't like how it looks, simply drag and drop another transition to its place to replace it. You can also expand or reduce the duration of the transitions by pulling or pushing its edge.