I made it red. Please feel free to change the color, add images, or generally design this so that you like the way it looks. If you want to add link, you need to click "compose" before writing. Then you click the "link" above. Once you do that, you can choose a word that should be highlighted, and add in the web address. You'll see. Here's an example. Counterpath

The same should work for adding images, or pdfs, or videos. If you are in "compose," you click on the icon for the thing you want to add and just follow the instructions from there.