Picture issues

I'm sure this is just me, and I'm an idiot. I've been having trouble posting pictures. I upload them to Imgur, but when I go to attach them to my posts they don't work. Is there a specific format I should use? I tried png and jpeg. Has time passed me by and should I take a computer basics class again?

Thanks.

What are you pasting into the image URL box? It has to be the URL of the actual image, not the page that they might contain it in.