You need to upload images to an image hosting site like imgur.com or postimages.org, then share the link. You cannot directly upload a file from your computer on this website because the site doesn't have a way to support it and it would probably be a security problem.
We can't see what you're trying to post since a file path like me/pictures/mypicture.heic is a location that's only on your computer, like how saying "in my bedroom" is a location specific to my house. If I say this to other people, it doesn't help them find what I'm talking about because they don't have access to my house (which is a very good thing) and they probably don't have the same item in their bedroom. That's why you need to put your picture in a public place that people are allowed to look at.
