Use Library for built-in sound effects and transitions. Sound effects become audio clips; transitions sit on a compatible cut between adjacent visual clips.
Add a sound effect
- Open Library → Sound Effects.
- Preview or search for a sound.
- Drag it onto an audio track at the desired time.
- Move or trim the new audio clip and adjust its volume in the Inspector.
Add a transition
- Put two compatible visual clips next to each other on the same video track.
- Open Library → Transitions.
- Drag a transition to their shared cut.
- Select the transition on the Timeline to adjust the controls that it exposes.
If a transition will not attach, close the gap, confirm that both sides contain compatible clips, and leave enough source duration for the overlap. Deleting or separating either adjacent clip can remove the transition.
See Timeline and Inspector and Clip Properties.