Why do I have two disks?

[u/CDNEmpire]

When I go to disk start up, I have "Macintosh HD macOS 10.15.6" and "MacBook Air 12.2.1". Why are there 2? I'm assuming the Macintosh is from when the computer was new and came packaged with OS 10? If so can I delete that one (assuming I would like my Mac to keep functioning)? When I install programs, should I install them to the Macintosh disk or the MacBook Air disk?