Customize general fields
You can add an arbitrary number of tabs to the entry editor. These will be present for all entry types. To customize these tabs, go to Options → Preferences → Custom editor tabs.
You specify one tab on each line. The line should start with the name of the tab, followed by a colon (:), and the fields it should contain, separated by semicolons (;).
will give one tab named "General" containing the fields url, keywords, doi and pdf, and another tab named "Abstract" containing the fields abstract and annote.
It does not matter how you capitalise your field names. In the entry editor's tabs, normally fields' first letter is capitalised, i.e. abstract is represented as Abstract, KEYwords would be represented as Keywords (DOI, ISBN, URL are exceptions in that all letters are capitalised). In the bibtex code, all field names use lower case: KEYwords is keywords in the entry's bibtex code.