Looking for an EASY Lightbox type Splash plugin

I am a relative newbie and am not sure what the correct terminology is. I’ve spent all morning looking for something that when people firs come on my site they have an image (lightbox?) that is on top of the site Home page that gives them a notice of a meeting. I have this notice as a jpg in my media library.

I’ve tried a few of the plugins but they either have ZERO explanation of how to use them or they are about having photo galleries, etc.

I tried WP Splash Image, but it doesn’t work and just gives me a giant gray box on top of my home page.

Is there not an easy way to do this?

Any help is appreciated.