How to sync voice over to video?

If you have multiple clips, you can adjust the size of the voice block to match every clip so that each voiceover plays at the right time. This can be done from the bottom timeline, as shown below.
Alternatively, you can add pauses in between your script from the top menu to adjust the timing of your voice with video.
The exact process applies to background music as well.
You can create empty text blocks to use as fillers to help sync your voice-over and video.