Formats are named after the file handle you are writing to. For example:

sub testf {
    my $object = shift;
    my ($sname,$class,$date,$classid);
    
    
    foreach my $item (@{$object->{'school'}}) {
        $sname   = $item->{'sname'};
        $class   = $item->{'class'};
        $date    = $item->{'EnrolDate'};
        $classid = $item->{'classid'}; 
        write STDOUT
    }

format STDOUT = 
Student Name @<<<<<<<<<<<<<<<<
$sname
Class: @>>>>>>>>>>>>
$class
Enrolled Date: @|||||||
$date
Class id.: @|||||||||
$classid

.

}

my $object = {school => [
                 {sname => 'Asname', class => 'Aclass', 
                  EnrolDate => '10/10/66', classid => 'Perl'},
                  {sname => 'Bsname', class => 'Bclass', 
                  EnrolDate => '10/10/66', classid => 'Perl'},
                   {sname => 'Csname', class => 'Cclass', 
                  EnrolDate => '10/10/66', classid => 'Perl'}
                  ]};

testf($object);
[download]

Gives:

Student Name Asname
Class:        Aclass
Enrolled Date: 10/10/66
Class id.:    Perl

Student Name Bsname
Class:        Bclass
Enrolled Date: 10/10/66
Class id.:    Perl

Student Name Csname
Class:        Cclass
Enrolled Date: 10/10/66
Class id.:    Perl
[download]

Personally I find printf simpler.

Update: Added blank line to break-up each record. Also note that the format cannot be indented, even though it is in a subroutine.