It sounds like the user has to switch the sound to come out of the correct speaker. This should happen automatically but sometimes it doesn't.
If using headphones, plug them into the audio jack on the Chromebook
Click down at the bottom right corner near the time and a little window will pop up
You will see a speaker on the left with a volume bar in the middle and an icon on the right. The icon on the right might show as an arrow or as headphones
Click the icon (arrow or headphones) that shows on the right
Under Output:
If you want sound to come out of the the Chromebook speaker, make sure the Speaker (internal) choice is checked
If you want sound to come out of the the headphones, make sure the Headphone choice is checked