A click popup opens only when a visitor clicks something: a button, an image, a link. Nothing interrupts the page, and the offer is only seen by people who chose to open it. That makes it the one popup style that grows an email list without annoying anyone.
This guide covers what click popups are good at, real examples, what to look for in a plugin, and the exact steps to open a popup from a button, an image, or a link. No code involved.