it is asking if and when you became covered by medicare. for the portion of the year you are covered by medicare you are ineligible to contribute to an HSA. if you did you must withdraw the excess contributions before the due date or be subject to penalties.
for example if medicare started in February 2020, you would only be able to make a pro-rate contribution for January. max for a single person over 55 is $4550. so you could only contribute 1/12 that amount.
