I noticed some people here don't know how it works, and I'm bored so I'm making a guide for those of you who need it. You're welcome.
First, find and locate the tiny image icon on the text formatting menu. It should be located in the 2nd to last column of the 2nd row. Click/tap it. It should open a menu.
How you proceed next depends on the visual content you wish to attach. Is it already a link? If so, you can simply paste that inside the url box on the first tab. If it is not, then you can navigate to the third tab that says upload on top, and upload your file, send it to the server, then use the url that generates to embed your visual content.
Have a video game character for making it this far.
I could make a better guide if I wanted to but I lost motivation.