How to add a transition between two clips?

Click the Transitions tab under the video library and you will find all transitions effects. Click a transition and you will see its effect in the Preview pane. To apply a transition between two video clips, drag it to the front clip. A black rectangle will be added to the end of the clip suggesting the transition is applied. To adjust duration of the transition, double-click the rectangle and operate in the pop-up pane.

Tip:  You can use the time line zoomer to zoom in the time line if the transition rectangle is too small to click.