I’ve posted a new video here that demonstrates how to shrink an existing partition with Disk Management and then create a new partition with the empty space in Windows 10.
Sometimes you’d like to have a separate partition for data or scratch drives to keep your data safe when you run backups or re-install an operating system or software. Other times you create new partitions to install a different operating system and do a “Dual Boot” with the extra partition. Let me know if you’d like to see a video or a post about dual-booting Windows 10 and Linux/Debian/Ubuntu.