Boy, do I feel like I've got egg on my face! I've been using computers for about 11 years, and I've never given a thought to external speakers being necessary to listen to YouTube videos, or PPS presentations...I guess I just assumed that since my computer makes dings and chirps and all the other sounds, that the sound from online sources would come from the computer's built-in speakers. I usually use headphones so no one around me will be disturbed by my stuff, but one day I had them plugged into the wrong computer and couldn't figure out why I didn't hear anything from the one I was working on. So I plugged in some speakers, and they worked fine. Then I plugged in my earphones into the right computer, and they worked fine. I'm obviously no computer geek, and only learn by trial and error (more error than trial, looks like). Anyway, I seem to learn something every single day, which is a good thing for a senior citizen.
Thank you all so very much for your answers to my silly question.
Shellbelle