You're seeing those questions because of your answer to a specific earlier question. You were asked if the taxable amount in Box 2A was the taxable amount used for prior years when you claimed this income. Or, if this is your first year, it still asks if 2a is the correct taxable amount.
If you said No, then what happens is you are put into a calculation called the Simplified Method to determine the taxable amount.
You do not need to do this unless you had contributions to your plan that were made with after-tax income, meaning you contributed money but received no trax deduction of any kind, and no reduction in your W-2 income, for those contributions.
If you don't think you qualify for the Simplified Method, go back and answer yes to the question described above.