This is amazing, more detail about how it works: http://b3s23life.blogspot.com/2006_09_01_archive.html?m=1
At the bottom of the document, it says "令和 6 年 3 月 21 日“, where the first two characters denote the Reiwa era which started in 2019 (=year 1 of the Reiwa era). 2024 then is year 6 of that era. And that's just what the next two characters denote: "6 年" = year 6. "3 月" is month 3 (the character symbolises a moon), and "21 日" is day 21 (the character symbolises a sun).