ePubs are based on HTML/CSS, if you want to edit your epub you need to learn those two.
It shouldn't take more than a couple of hours learning the basics to get your sorted. However, untill that time comes you can use this:
<p><img src="PATH_TO_YOUR_IMAGE"/></p>
<p>YOUR TEXT</p>
As for the easy solution, you could use Sigil, it has a book view edit mode so you can edit your book kind of like you edit your microsoft word documents.