To enroll in a payroll service, business owners need to gather key information about themselves, their business, and any employees. This includes personal details like names, addresses, Social Security numbers, and email addresses. It also requires payroll information such as hire dates, pay amounts, deductions, and tax withholding status. Business owners should have their business bank account and Federal EIN numbers ready. For businesses registered with the IRS, the EIN can be found on past tax documents or obtained for free from the IRS website.