How do I insert an audio into a slides presentation?

Save the audio files to your desktop from your audio recording software.

To record audio on Google slides, follow these directions:

1. Upload to your Google Drive any audio you need use to annotate a specific slide, naming the file consistently with the slide you will use it with.
2. Under Google slides, use the Insert menu, and select insert audio.

Note, Google slides may only support specific audio formats. for that you will have to look at Google slides documentation.

There are numerous audio conversion applications, including Mpeg4streamclip.

What app is your presentation in?

Are you using Apple Photos for slides, or what program are you using?

Maybe a question for Google Slides Help.