Unmute your device, check video player settings, unplug headphones
There are a few settings to check if you are unable to hear the videos. First, check that your computer is not muted; you can often check this through your settings or by selecting the speaker icon at the bottom of your screen. You can also check to see if your sound is already being sent to connected speakers or earbuds.
If your computer isn't on mute, and you still don't hear sound, check the video sound. Hover over the video to see the sound options. This looks like a set of increasing height bars at the bottom of your video viewing area. You should see those bars in color; if they are all dark grey, your video is muted. You can click on those lines to unmute.