The MacBook Air hasn't really been touched since 2015 except for a little spec bump in 2017. Now Apple has brought the MacBook Air into 2018.
When Apple released macOS Mojave or macOS 10.14 in September they redesigned and brought many apps from iOS to macOS. Many of these apps use the same design and operate the same as their iOS counterparts.
Markup tools was a feature added in iOS 10 that allowed users to use basic editing tools for images. They started out being very limited but have now expanded to many other places around your iOS device. The places it can get use the most are in photos when taking screenshots and saving PDFs in Safari.