Documents is where your paperwork accumulates. The W-9 can be filled out and signed in the app, on the IRS's own form; the family sees that it is on file with only the last four digits, and the full number never travels with your record. W-4 and I-9 open the official IRS and USCIS blank forms to fill and upload. Every document has a status pill, Replace, and an expiry date where it applies, and you can add other documents.
Working for an agency that keeps your file on ExpressAgain: your agency's W-9, or W-4 and I-9, are filled and signed in the app on your own Team file, not in a family's home. See Your W-9, W-4 and I-9 for your agency.
The Documents tab also shows the paid-to-you line for the year. An independent professional paid more than the IRS reporting threshold in a year is flagged for the family's 1099-NEC; an agency-billed invoice counts for the agency, not the person whose hours it lists.