Schema markup is a shared language that search engines created in order to provide "rich results" to users' searches, especially on mobile. In this tutorial by Jose Ocando, you'll learn how to add Schema to a Webflow project.
Do you need your modal to only come up once per user? this is the tutorial you are looking for from Pixel Geek.
Learn how to add custom code from CodePen to Webflow in this tutorial by Joseph Berry.