First of all, in your case the problem is your reputation. As a [new user](https://askubuntu.com/privileges/new-user), you cannot post pictures. We will update the posts for you, until you gain the privilege to do so.

The simplest solution, once you can, would be clicking the `img` button on the editing form, or using the shortcut it shows (<kbd>Ctrl</kbd>+<kbd>G</kbd>):

![Screenshot 1][1]

This then prompts you with another mask which allow direct upload and linking and thus automatically inserts the necessary code:

![Screenshot 2][2]

If you do not want to use this mask, however, you can click the `Images` button on the help bar, which shows the markup:

![Screenshot 3][3]

  [1]: https://i.sstatic.net/Ujnfk.png
  [2]: https://i.sstatic.net/nfSgw.png
  [3]: https://i.sstatic.net/vrsIE.png