Judging by your post history, it seems like you want to display an image that is currently on your computer. That's not possible, you have to host is somewhere on the internet first. This can be done by uploading it to an image service, such as
https://imgur.com/ .
Just click on Computer under Upload images, browse to the file, select it, click Start upload, and wait for the image to be uploaded. You will now see your picture with a bunch of links on the left, copy the one under "message boards", paste it in your post, and you're done.
You can also copy the Direct link, and manually type the img tags.