I have looked all through the User Guide, and nowhere can I find details of what information exactly each of the fields refers to - only the standard author, date etc are covered. It might be my imperfect knowledge of referencing - but it would be really useful to know the difference between document number and report number, for example, and what is the Type field? I also don’t know what referencing type to use for newsletters and working papers, for example. Are there any descriptions or guidance on fields and reference types out there?
It would be good for you to determine first what publication you are targeting your writing to, and then to start with that output style. That will tell you what kind of information you need to fill in -in your records, and it usually becomes pretty obvious at that point. You will find that there are reference types to cover many, but not all of the specific materials you may want to refer to in your writing.
A librarian may be able to point you to a reference guide, such as MLA
This has always been a drawback with EndNote, especially for the new or infrequent user.
As Leanne suggests, you need to choose the output style which you will use, and then open it for editing. Go to Edit>Output Styles>Edit [name of style].
Look at the Bibliography>Templates section of the style to see which reference types are supported, and which fields within those reference types are supported.
Often this will be enough to tell you which reference types and fields you need to use to get a correctly formatted reference. Of course you can add extra fields or new reference types, but that’s a little more complicated.