I'm having a lot of trouble with this, and it's a little embarrassing

How do I link an article and have it show the thumbnail and title
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You should be able to copy a website address and paste it into the body of the post.
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^ This is right. Bear in mind it won't show up correctly in preview, and after you post it you'll have to refresh your browser before it shows correctly.
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Yes and also I think the result can depend on whether the linked website is equipped to serve a picture.