The suspect (a person thought to be guilty of a crime) appears before a magistrate court judge to have the charges brought against them explained and to determine if they are to be released on bail (the temporary release of a prisoner in exchange for security given for the prisoner's appearance at a later hearing). this paragraph is describing what?

This paragraph is describing a court hearing for a suspect where the charges against them are explained by a magistrate court judge and a decision is made regarding their bail status.

is it describing the preliminary hearing

Yes, that is correct. The paragraph is describing a preliminary hearing, where the suspect appears before a magistrate court judge to have the charges explained and to determine if they will be released on bail.

The magistrate judge determines if there was a crime committed and if there is probable cause (a reasonable ground for supposing that a charge is well-founded) that the suspect was involved with the crime.

Yes, that is correct. During the preliminary hearing, the magistrate judge will review the evidence presented by the prosecutor to determine if there is probable cause to believe that a crime was committed and that the suspect was involved in the crime. This determination will help decide whether the case should proceed to trial.