A 1099 form is an informational form you receive – not a tax document you fill out. If a business or government entity sends you money during the year that is reportable on your taxes, you should receive a Form 1099.
There are many different kinds of 1099 forms. For example, 1099-DIV informs the IRS that you were paid potentially taxable dividend income; Form 1099-C reports the cancellation of a debt, which is sometimes a taxable event and Form 1099-MISC reports payments to independent contractors. Dozens of special situations call for a Form 1099 but they all cover payments you receive that may potentially be taxable.