An affidavit contains a chronological summary of the facts that establish probable cause. An affidavit is not as complete as a police report and only has the essential details to establish probable cause.
The completed affidavit is submitted to a judge and they determine if probable cause exists. If the judge agrees that probable cause exists, then they will sign and authorize the search warrant which is filed with the court along with the warrant.
Defendants do not receive a copy of the affidavit at the time the warrant is served. They can receive a copy of it later in court. In the field, the defendant is only provided with a copy of the warrant.
Below is a criminal law sample affidavit: