I'm quite the technological blimp and was wondering if anyone could advise me please, in plain simple English, how to attach a "badge" to a photo to be posted online???

Do you mean a watermark? Not sure what a badge is. 

Here's a link to watermarking in PowerPoint, explains it better than I could:  

https://support.office.com/en-us/article/Add-a-watermark-to-a-photo-with-PowerPoint-2374ae14-b50e-4a7f-9d06-bd82206e16ec

I also use the iWatermark app on my phone 

Thank you hippiecac. I've looked through what you sent me. I don't know whether they're the same or not. I'll need to check with my sons, or perhaps my grandson; he's 12 and becoming quite a computer whizz.