How do you post images on mobile?

I saw a tutorial on how to post images, but it looks like it's only available for computers. I don't have a working computer :(. I just have my phone, and I want to post some of my art. I figured out how to "code" the HTML, but when you're on mobile, it doesn't give you the option to use HTML. Maybe it does, and I just haven't figured it out.... Can anyone help me?