[Koha] Marc Framework

I am using Koha on Windows. I only have one, the default MARC framework. On checking the MARC structure, it has the tags I require like 852$c, 952, 037$n, etc. However, when adding biblio or editing the Marc values of any book, these Marc fields are not displayed. Only some of the fields from the MARC framework are available for editing. How do I get the required Marc fields for editing and adding data? Thanx Nitin