How to open a modal window?

Question

css

Hello. Tell me how to open a modal window, if I made it on another page and I need to call it directly into the current one?
I made it so that this modal window in index.php does not interfere because I don’t like it.

Answer 1

I did not understand this: "so that this modal window in index.php does not interfere because I do not like it."
If I understood correctly: does your modal window exist separately on a separate page?
Then connect this page with an include where you need it via php