Normal build is the final stable version of Windows 10 currently available for everyone to install and use. For example, the Fall Creators Update is known as build 16299.15. Every month or so, when Microsoft releases new updates the second part of the build number after the period get bump up. For example, as soon as the Fall Creators Update released, there was an update that bumped the build number to 16299.19.
“Redstone” is just a codename for the builds that Microsoft releases to participants of the Windows Insider Preview program to test upcoming features and changes. These builds are not publicly available to everyone. These builds are rough and they contain bugs and issues because in this stage features and in development.
- Redstone was the codename for the development of Windows 10 version 1607.
- Redstone 2 was the codename for the development of Windows 10 version 1703.
- Redstone 3 was the codename for the development of Windows 10 version 1709.
- Redtone 4 is the codename for Windows 10 version 1803.