I am going to assume that you have no attorney. As an attorney is an officer of the court, they can serve a subpoena without the court's approval. But without an attorney, a subpoena has to be approved by the Court.
One fills out the form and then files it with the Court (this can be the intake clerk for the district clerk, or, the court's clerk directly - check with the court to see which they prefer for subpoenas).
Then, the clerk/Court has to approve the subpoena. This means that once the subpoena is filed with the Court, one calls the clerk of the court and asks for the Court to endorse the subpoena. At this point, the clerk will look over it and will endorse it if it is done correctly. Sometimes the Judge of the court also prefers to review the subpoena before approving it.
Assuming it is approved, one then serves the party with the subpoena.
You can see a summary of the rules HERE.
Gentle Reminder: Please, use REPLY or SEND button to keep chatting, or RATE POSITIVELY and SUBMIT your rating when we are finished. You may always ask follow ups at no charge after rating.