You just add them to the description ... eBay descriptions can be written in HTML, and images can be added if you have somewhere to host them (TinyPic.com is free and pretty intuitive to figure out how to use; of course if you have your own website you should host them there.)
I posted a template I use for many listings Link hidden: Login to view
a while back. Have a look at it, and if you want to use it and need some help customising it feel free to ask. I'm happy to walk you through it if you need it.