<img src="insert direct link here"> is the tag for adding images pretty much anywhere in this site.
The image will need a direct link to it, which you can get by searching up image hosting sites and uploading your image there (unless you somehow have the direct link already, in which you don't have to do all that). Here's an example:
https://i.postimg.cc/Rhn8TpRW/Sans-titre-210-20240403204252.png is the direct link I'll be using for my image. In order for the image to appear, I type <img src="https://i.postimg.cc/Rhn8TpRW/Sans-titre-210-20240403204252.png">
Using that tag, this image will appear in place of it:
