You need the Rotato app. It's free with an unlimited trial, and available in a Pro version, too. The only difference between the two versions is an ear tag (watermark).
After you pay, you get an email with a download link.
Once you purchase, you receive a personalized link to a ZIP file. Double click the zip file and then open the Install app inside. Rotato will add all the templates to your template library.
You can change virtually everything in this template bundle. You can use any device in Rotato, change the screen contents on the device, use a video, use a screenshot. This also goes for the web page template. You'll get the entire source code and the entire Webflow template. You can change fonts, contents, colors, layout, everything.
A 10 second movie typically takes a little less than 10 seconds.
No. Rotato is an offline, local-only tool. This also goes for these templates. No designs are uploaded to the internet by the app.