Upon entering the Minecraft server, click on the message in the chat or type /audio. This will connect you to the proximity voice chat. 

Click "Yes" on the message on your screen, and you will be redirected to a web page. 

On this webpage, click on "Start session with voicechat." 

After clicking "Start session with voicechat," you may be prompted to allow access to your microphone. Click "Allow" to grant permission. 

Congratulations! You are now connected with voice chat.