'our' gets you a "package global", accessible outside the package via <sigil>PACKAGE_NAME::var_name, or a variable that can be "imported" into your program's namespace.

Hopefully, this code will clarify:
FOO.pm

package FOO;
use warnings;
use strict;
use Exporter 'import';
our @EXPORT_OK = qw/$bar $baz Baz_Get_Set/;

our $bar = 42;  # Package global, visible as $FOO:bar
my  $baz = 66;  # Not visible outside FOO - needs accessor sub 

sub Baz_Get_Set{
    defined $_[0] and $baz=$_[0];
    return $baz;
}
1;
[download]

pm11149136.pl

use warnings;
use strict;
use feature 'say';
use lib ".";
use FOO qw/$bar $baz Baz_Get_Set/;

say "\$bar (an imported 'package' variable)=",$bar;
say "\$bar (accessed explicitly via package name \$FOO::bar)=",$FOO::b
+ar;
$bar="Set via caller";
say "\$bar (accessed explicitly via package name \$FOO::bar after sett
+ing via imported var)=",$FOO::bar;
say "\$baz (direct attempt to access package 'my` variable)=",$baz; # 
+This returns UNDEF 
say "BAZ via getter/setter=",Baz_Get_Set(); # Nothing passed - this is
+ a GET
say "BAZ get after setting to 55=", Baz_Get_Set(55);
[download]

OUTPUT:

bash-5.1$ perl  pm11149136.pl 
$bar (an imported 'package' variable)=42
$bar (accessed explicitly via package name $FOO::bar)=42
$bar (accessed explicitly via package name $FOO::bar after setting via
+ imported var)=Set via caller
Use of uninitialized value $baz in say at pm11149136.pl line 11.
$baz (direct attempt to access package 'my` variable)=
BAZ via getter/setter=66
BAZ get after setting to 55=55
[download]

</c>