This passage is talking about offices. As far as the tongues and interpretation here, it is talking about those with the gifts of diverse kinds of tongues (for messages FROM God to the congregation given to a very few), and interpretation of tongues (interpreting the message FROM God also given to a very few). Not everyone has these offices for the profit of all. BUT,
All those who believe receive the individual sign gifts of Mark 16:16-18 - Tongues, casting out demons, healing, and divine protection. Notice, interpretation of said tongues is not mentioned. That is because our prayer/praise language doesn't have to be interpreted as God, the receiver of the prayer, knows what you are saying even though you don't. But you can pray for the interpretation even without having the office of always receiving the interpretation of tongues - either one - 1 Cor. 12 or Mark 16. For instance, I have the gifts of prophecy and healing, but have not been given the OFFICE of Prophet or Healer. All Jesus said to me is that He is giving me the OFFICE of Teacher, but with other gifts I need.
Don't feel embarrassed to not know what 1 Cor. 12:30 is specifically talking about; there are Pentecostals that don't know there are two types of tongues, and make the same mistake in not recognizing that this is talking about an OFFICE.
cc:
@Truman