When editing in the Simplified editor, you can easily add transitions between clips. Simply select the clip, and click on the transition icon either to the right or left of the clip. A “Cross fade” transition (1s) will be added by default.
To change the style of your transition, click on the transition icon between the clips. This will open a popup that will allow you to change the style and duration of the transition effect. You can also decide whether to apply that style to all the transitions in your video.