You can trim handles from outgoing and incoming shots and use them to add a dissolve.

To create handles for a dissolve:

1. In the Storyboard, select the shot to the left of the cut point to which you want to add a dissolve.
2. In the Edit menu, enable Retrim.

   
   

3. Enable Dissolve, and then drag the Dissolve slider to set the duration or right-click the slider for the pop-up entry.

   Frames are automatically trimmed from the tail of the outgoing clip and the head of the incoming clip.