How to add a splash page on my wordpress site? I have Grand Portfolio, Responsive Portfolio theme

I have purchased and enabled the Grand Portfolio |
Responsive portfolio, and everything is working great. However, I want
to add a simple splash screen to my website. I want a splash screen that
does not include any menu links, I only want to have a background
image, and a button link to my main homepage. Is there any article or
information on how to do this?Thanks,Mo