[Koha] error in MARC check

[hbotero]

We are trying to begin to use KOHA.  Now we are working with MARC structure.
When we run "MARC CHECK" we got the following errors:

-----------
itemnum The field itemnum MUST be mapped
The correspounding subfield MUST be in with -1 (ignore) tab

itemtype NOT mapped the biblioitems.itemtype field MUST :
be mapped to a MARC subfield,
the correspounding subfield MUST have authorised_value="itemtype"

homebranch NOT mapped the items.homebranch field MUST :
be mapped to a MARC subfield,
the correspounding subfield MUST have authorised value="branches"

holdingbranch NOT mapped the items.holdingbranch field MUST :
be mapped to a MARC subfield,
the correspounding subfield MUST have authorised value="branches"
-------------

We would appreciate whether some one can help us informing where to fit 
these errors.

Thanks

H. Botero