Retirement distributions are generally taxable. The check box means that the payer was unable to determine the taxable amount, so it is up to you to figure that out. In the case of an IRA, it would normally be the full amount. For an annuity it appears to be more complicated. Your payer should have provided instructions with the 1099-r. You can find the IRS instructions at
https://www.irs.gov/pub/irs-pdf/i1099r.pdf.
