Can anyone tell me how to insert a screenshot into a post? (They're asking me for the image URL, which I don't know, since I just took a screenshot of my screen.)
You need to upload the image somewhere. Websites like imgur don't even require registration. Then you post the direct link with the insert image button. Ideally you scale the image to 500 or 600px.
Use the quote function to see how it's done (this is scaled to 400; the unscaled orginial size would blow up this page):
Imgur.com doesn't work on my computer. I used imgbb.com instead, and I am able to post the link to the image which, when clicked, sends you to a tab with the image on it (among other things). Probably not as good as imgur.com, but it'll have to do. Thanks anyway!