i use a phone. not sure if its the same on pc, but in the 'toolbar' (where you can change font, bold, etc) there is a little square with mountains and a sun. click that, paste in the link, and it embeds the pic in ur post.
Download to your computer then attach it in "full view" mode. Maybe it can also be done without downloading to your computer, I don't know.
THAT FACE YOU MAKE... ...when you discover gifs. Hahahha, find that button up above the field where you type into it looks like a tiny box with a mountain and a small sun, says "image" when you hove over it - click and copy/paste the url of a gif. If the gif doesn't show up when you hit ok then the source doesn't like hotlinking so find another.