I'm trying to add a from by click option (not in layerslider) 

I need help with the instructions below, please. I get stuck at the custom class name and it does not work. 

If the button is not part of a slider, you can use the Project Settings → Layout → Popup → Open By Click option. That option field expects a selector to target the button that will open the popup. You need to add a custom class name to the button, for example, "open-download-popup" (without the quotes). Then, you can enter the same class name in the option field described above with a dot at the beginning: .open-download-popup. The dot signifies that you're looking for a class name. You can use a hash mark if you apply an ID attribute to the button instead of a class name.

I'm still not understanding. I added the short code in the button but when i click on it, it takes me to 404 error page. 

I flushed my cache on site and web browser. Still not working. Any other ideas? 

That worked great! Thank you!