Grand juries can use the court's power to subpoena evidence.
The subpoenas are actually issued by the court clerk's office. The prosecutor will go to the court clerk's office and obtain blank subpoenas. You comply with a grand jury subpoena by doing what it tells you to do. Quashing the subpoena means the court declares it null and void, so you don't have to comply with it. A court would, for example, quash a subpoena if you could show that making you comply with it would violate your constitutional rights under the First Amendment.