Does missing one birth control pill mean you are unprotected for that day or what does it mean?

Still protected: Birth control works mainly by preventing ovulation. If you miss a day, take the pill as soon as possible. You will not have ovulated and are still protected. If you miss two days, you are now at risk and should use secondary contraception such as condoms or abstain from sex for 7 days. (if you miss 2 days in your third week, start a fresh pack at the end of the week instead of taking the placebos).

Depends on type: If you are on a progestin-only birth control and you miss a pill then yes the risk of pregnancy is high ( in this case take the pill /use a back up method condoms/spermicides for the next 48 hours). On combination progestin/estrogen also risk of spotting/pregnancy, take the missed pill plus that days pill and use a backup method. Always practice safe sex use condoms.