How to add a pop-up when opening the page?

#1

I would like to add a pop-up as soon as I enter the site. I’m starting from scratch

#2

Technically, you’ld fire one with Javascript I assume?

In practice, they are seen as annoying by most users.

Also; this is not really kirby-related I think?

#3

This.

Edit: If you ask google this question, you will find tons of tutorials how to achieve that. But I’d really think twice if this is desirable.