As stated on the W-4 that you give to your employer for tax withholding -https://www.irs.gov/pub/irs-pdf/fw4.pdf

I claim exemption from withholding for 2019, and I certify that I meet both of the following conditions for exemption.
• Last year I had a right to a refund of all federal income tax withheld because I had no tax liability, and
• This year I expect a refund of all federal income tax withheld because I expect to have no tax liability

If this applies to you then write Exempt on the W-4, otherwise enter the number of allowances on the W-4

Use this IRS withholding estimator - https://www.irs.gov/individuals/tax-withholding-estimator

Assuming you are referring to exemption from withholding on a W-4, it is generally not recommended. But you can lower your taxes withheld by claiming all of the allowances that you are entitled to. Use the worksheet on page 3 of the W-4 form to complete the allowances.

Page 1, paragraph 3 of the W-4 form explains the qualifications for exempt status.