Hi @Marcos_Custodio, thanks for your update. The best thing to do, in these kinds of cases, is to create a new blank site, and then look at the instructions on the plugin page, and see where things need to be installed. Once you have a test site working, you can then update your target site with the same settings etc.
CSS customizations can be done in the Designer Editor or can be pasted into the Head of your site.
jQuery code goes in the footer of your site.
Elements used for the effect in the body of your page, are created in the designer, or pasted in using an embed object (to paste in html tags that the plugin uses).
Every plugin is different Don't be afraid to experiment If you have questions while you are trying to put it together, then ask here in the community You have done this already, so you are halfway there
I made a quick example particle parallax effect site using this custom plugin, that you can clone, and see how it works. You will need to copy the js file that is linked in the footer, to some storage that you can link to, like dropbox.
Note: We do not support custom code, but we are happy to help when possible
I hope this helps. Cheers, Dave