[Koha] A simple question about Class

[Yaogeng Cheng]

In http://hlt.katipo.co.nz/, if you search by "Understanding your brain" by
Title in the cataloge page. Then you click the TITLE Understanding your
brain, You get the Class J612.82. How did J get into it? What did J
represent and how can I input it into the Koha system?

Thanks a lot!

Yaogeng