The version of Movie Maker that will work with Windows 8.1 is part of Windows Essentials 2012. The program was retired more than a year ago so your only option is to install an archive copy of the program, though do realize it will not get any updates from Microsoft.
Where to get a Safe Download of Movie Maker
If you had upgraded to Windows 10, you could use the Photos App that is part of the Fall Creators Update to create your videos.