No worries. You can upload images directly, however (most) instances limit sizes to 100kB. This also uses up the instance's limited resources (every federated instance will also be accessing this). So it's better to use a link from somewhere else.
You need to use the full link I gave, https://i.imgur.com/KSQR0KU.png and put that in the URL for your post. Clear the body, put the URL at the top, leave the title.