While playing VRC keep in mind that the game has it's own audio settings that may need to be adjusted.
If you are having trouble hearing people make sure you have their volume turned up by:
Open the VRC menu and click the speaker icon.
Ensure the Voices volume is turned up as well as the Master slider.
Make sure you have the correct mic selected by:
Open the VRC menu and select the speaker icon.
Scroll down to Microphone and select Change Device.
Esure the correct Microphone is selected and try again.
Still no luck?
Try making sure your not muted in game.
If you see a red microphone with a line through it the means you are muted.