Take a look through perldoc Win32::ODBC this will introduce the concepts you need to follow this code and define the methods used in your snippet.

Essentially it creates a string of the stored procedure and argument(s) and then makes a single row selection from the results of this procedure which it returns as a hash and checks for a value in the field specified in the variable $strResultField

In this specific caseExecStoredProcedureArg1("pr_CustomForPV",  "$VersionID,$AutoNumber", "IsCustom") it runs the pr_CustomForPV procedure with the values in $VersionID and $AutoNumber and checks to see if the IsCustom field is set