If you're able to join the event but are not hearing the audio, it could be due to various issues.

First, check that your computer/mobile device volume control and headset are working properly and neither is set to 'mute.'

If you've confirmed your technology is working you can test your audio by clicking the arrow just to the right of the microphone icon in the toolbar and if you don't see the toolbar please wiggle your mouse or touch your screen (when using a touchscreen device like smartphone) to wake your screen and for the toolbar to be displayed.

Adjust speaker and microphone settings in Zoom during a meeting

Instructions for modifying the speaker and microphone settings in Zoom during a meeting.

Zoom_Audio_01
Click the '^' next to the "Mute" button to display further settings

Zoom_Audio_02

Select "Audio Settings..."

To change which speaker or microphone your computer is using for the meeting, select the appropriate device from the drop-down menu. Which device should be used will differ depending on the computer.
Zoom_Audio_03

You can also adjust the speaker and microphone volume here. Turning one or both down can help stop echoing

For more detailed audio specifications, check out this Zoom support link:

https://support.zoom.us/hc/en-us/sections/4413768837517-Audio-Settings