How can I write the perfect explainer video script?

Hi, Im about to finally finish the landing page for my first big product. In order to quickly convey my product to my audience I want to write the best possible explainer video script, which will then be passed on to a designer over at fiverr.

Im aware of the basic what, how, why approach but im struggling to link both the different scenes and script together.

What helped you guys solve this?