W-4 form is used to determine the amount an employer must withhold from employees' wages for tax purposes.
W-9 form is used when an employer hires a contractor and pays $600 or more during the year. The form must be filled out by the contractor and provides basic information about the business or contractor.
I-9 form is used to verify the identity and employment authorization of individuals hired to perform employment in the US. All employers in the US must complete and submit an I-9 form for each person they hire; that includes citizens and non-citizens.
FORM 1099 NEC
1099-NEC from is used to report compensation paid to non-employees. Any business that pays more than $600 in a tax year to someone other than their employee is required to file a 1099-NEC with the IRS.
Schedule C is a tax form used to report income or loss of a business operated by an independent or a single member limited liability company.