Homepage popup

Hello!

I would appriciate some help with the popups!
I’d like to make a fullscreen popup for my homepage, what is coming up in the 0.second.
i have got a blog and a webshop too, and i want to give the choice to the visitor to decide where to go next.
I tought that it would be a good idea, to use a popup window, with two pictures. One of them are leads to the webshop (sub-domain), and the other one closes the pop-up.
I have found a plugin.
https://wordpress.org/plugins/full-screen-popup/
The problem is, that i dont know what to do to close the popup with a picture. What script do i need, and where should i paste.
Thanks for any help!!!