Simply put, a subpoena is a request to a person or corporation to either A) provide documents related to a legal case, or B) appear in Court (or at another location) to provide answers to questions “on the record.”
A subpoena does not mean you are in “trouble.”
The requests found within a subpoena must be either obeyed, or the requests must be properly contested in the Court that issued the subpoena. Failing to respond, or worse, destroying any documents that were sought, is a terrible mistake.
If you have received a subpoena and are unsure of what your response should be, contact an attorney who practices law in the jurisdiction (usually within the county) of the Court that sent the subpoena.