This is your main page with the popup window code.

Open 'View Source' on this page and copy the code where the 'script'
begins and ends, paste that into the HEAD section. Put the URL
'link' to your popup page in the script code where I have 'popup1.html'.
Adjust the Width and Height for the popup window and
position the popup to open on the screen to your needs.

Build an html page with your title, background image and text and/or images.
Name the popup window popup1.html or what every you want.
Put that page name as the link in the page with the popup code.
And be sure to include a close window button.
INPUT TYPE="button" VALUE="Close Window" onClick="window.close()"