Good enough biblio record/
A "good enough" minimal bibliographic record
This is what could be keyed in for a "good enough" minimal bibliographic record in MARC21, that includes information necessary for identifying a particular edition of a particular title. Note: "yyyy" in the 008 means key in the same date as in the 264 field. This includes the minimum information necessary to identify a particular edition of a book, and where you would look for that information.
IMPORTANT: Leave the "double dagger" symbol and the lowercase letters that follow them, e.g., "‡c". Leave these untouched unless they cause errors in the Koha Bibliographic Record Editor. (If they cause errors, you may need to re-key the double-dagger symbol with a "ctrl-d"). They are important--they indicate subfields.
000 00830am aa2200205a 44500 003 CSfMM 005 20200602100802.0 008 200601 s yyyy xxu||||| |||| 00| 0 eng d 040 _ _ ‡cUDU 100 1 _ ‡aSurname, Forename. 245 1 4 ‡aThe title :‡bsubtitle /‡cAuthor name as it appears on title page. 264 _ 1 ‡aCity of publication :‡bPublisher name as on title page,‡cdate of publication or copyright date. 300 _ _ ‡aLast numbered page in book :‡billustrations mentioned here if present ;‡crounded up height of book in cm 500 _ _ ‡aNotes about the book or the record; this is a "good enough" record. 650 _ 4 ‡aTopic subject heading. 651 _ 4 ‡aGeographic subject heading. 700 1 _ ‡aSurname of another person, Forename of another person. 710 2 _ ‡aOrganization or corporate name. 740 0 _ ‡aTitle variations.
You can find out what the numbers and subfields (the double-daggers with little letters) mean from the MARC21 Format for Bibliographic Data at the Library of Congress.
What's the difference between a 100 and a 700? Practically, the 100 field will usually display above your description, the 700(s) below your description. In cataloging, the 100 is called the "main entry" and the 700 an "added entry," and this developed out of card catalogs, originating back when card catalog cards were hand-written and/or hand-typed, and there is a brief description and history here under "Manual catalogs and printed products."