For other tags, go to this html guide page.

Paragraphs:

To split the text into paragraphs, place <p> at the beginning and the end of the text.
example: <p>This is my first paragraph<p>

Line breaks:
To place an empty line between items, use <br>.

Images:
Embedded images must be online somewhere, not on your hard drive. First, find the image you want. Then, right click on the image and choose "Copy Image Location". Back on Google Earth, use <img src="url">, pasting the location of the image between the quotes.
example: <img src="http://earth.google.com/images/aiabanner.jpg"> inserts this image moz-screenshot.jpg
galaxy.jpg