Applying a Transition Between Clips
Step 1: Add clips to track
In order for the transition to work the clips must be on the same track and next to each other.
Step 2: Go to the effects panel
Expand the “video transitions” folder
Step 3: Drag the transition
Drag the selected transition between two clips until you see the center cut icon.
Step 4: Play back
Preview the sequence to make sure it looks okay!
Tip: By default the transition durations are set to one second. You can change the duration in the effects control.
– Kathleen Meriano