I don't know how to structure my talk, how to practice etc. I think I need to write a script of all the things I want to say then build the slide to support that script. Much like writing a blog post, or how many youtubers create videos. Is that a good approach?
One generally helpful tips is to learn details about the conference venue early, the more you know about the presentation format, the better you can prepare.
Try and discover if there's a teleprompters or a second display output setup to provide notes, a script and/or a preview of the presentation. Understand if you'll stand behind your laptop, have a remote to control it, or a pointer for the screen, and consider the implications of these constraints. What if you want to show a website but you don't have a mouse to close back out of it, or one video in your presentation is particularly loud/quiet and you can't quickly adjust volume down or up enough.
Even little things like setting expected aspect ratio or maximum resolution can smooth out the process of plugging in devices or properly displaying a slide/demo. If you can't get this from the hosts, try finding videos/slides from prior conferences to get a reference and review the standard production value and audience level of understanding.