See the documentation for Exporter. Basically anything you list in @EXPORT_OK will be available for import by name into other modules which use the exporting module, and anything you list in @EXPORT will be imported automatically into useing modules. It's generally considered better style to use @EXPORT_OK, or to use a named tag in %EXPORT_TAGS, but if the whole purpose of your module is to provide constants @EXPORT may be OK.

Your module might look something like this:

package MyConst;

use warnings;
use strict;

use base 'Exporter';
use vars qw(@EXPORT_OK %EXPORT_TAGS);
@EXPORT_OK = qw($const1);
%EXPORT_TAGS = (all => \@EXPORT_OK);

# ...
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And the module using it would begin like this:

use MyConst qw(:all);
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