Audio playback of terms' pronunciation can be configured in the Audio section of the Settings page.
For Japanese terms, Yomitan provides a preconfigured audio source. More audio sources can be added in Audio > Configure audio playback sources. They will be checked for pronunciations in the order they are listed.
For other languages, the Yomichan Forvo Server Anki add-on is one way to get pronunciation audio. After installing it, add a Custom URL (JSON) audio source with the URL http://localhost:8770?term={term}&reading={reading}&language=en (replace en with the desired language's ISO code).
With at least one working audio source in place, you can click on the 
speaker button to hear the term's pronunciation. When searching for audio, the sources are checked in order until the first valid source is found. Right-clicking the speaker button allows choosing the source manually. If no audio is found, you will hear a short click instead.