All your fields will appear as new columns when you export a spreadsheet:
The “fields” feature is new. We know there’s plenty of pizzazz to add:
Right now, we only support single-line text fields: no dates, numbers, geo-coordinates, or so forth. As a workaround, format your text values carefully (e.g., use YYYY-MM-DD for dates) so your spreadsheet program can grok them.
Overview’s search feature doesn’t examine field values.
You cannot create fields or write to fields using the API. (You can read field values with the API, though: they’re in document.metadata.)
You can only set metadata on one document at a time.