Creating a popup for my website HELP!

Question

I want to create an ad that pops in on user interface whenever they enter my website.
I want the popup to contain a link on the image or gif that links to my Spotify playlist.
How do I make this popup?
If you can, can you provide a easy answer?
Thanks!

Answer 1

create an element with position : absolute; to exclude it from main flow and keep it hidden on background with display : none; and show it whenever you want with display : block; (CSS)

Answer 2

If you want a popup in JavaScript use alert("");