The audio/video player doesn't work
If you don't hear any sound when you click on the audio/video player within a lesson, make sure that the sound works on your computer or mobile device - speakers or headphones must be connected and volume shouldn't be too low! Also, check that the sound of the player is not muted or too low.
If the problem persists, try reloading the page. You may also need to update your current Internet browser. We recommend Google Chrome or Mozilla Firefox.
If the player still doesn't work, it is possible that your browser is not configured for certain audio formats (mp3 or ogg)... A simple Google search can help you solve this problem. Good luck with that!