Windows Live Movie Maker was part of Microsoft Essentials 2012 and the landing page for it has been removed:
There is some details about using the Photos App in Windows 10 however it offers an inferior experience. Hopefully they will amend this later on in Windows 10 or make a separate Movie Maker App.
It can be unofficially downloaded from the following (web.archieve.org is a service which backs up links from old websites).
English (UK):
English (US):