enable paging for ed_classified module

Can sumone suggest me the way to implement paging in ed_classified module or in drupal in general?

for e.g i've got following code in my module:

if ($pager = theme('pager', NULL, _ed_classified_variable_get('ads_per_page', 2), 0)) {
$content.= $pager;
}

but, my control never goes inside this statement, i find this line in almost all of the modules, but, since m just a beginner when it comes to drupal, m unable to understand it.

Please suggest me a way to enable paging.

Thanks,
kul.