public function renderSitemap()
{
    // Get an ElementCriteriaModel from the ElementsService
    $criteria = craft()->elements->getCriteria(ElementType::Entry);

    // Specify that we want entries within the ‘locations’ section
    $criteria->section = 'locations';

    // Loop through any entries that were found
    foreach ($criteria->find() as $locationEntry)
    {
        // Here we’re building a path using the entry slug.
        // This might match a custom route you’ve defined that
        // should be included in the sitemap.
        $path = 'cars-for-sale-in-' . $locationEntry->slug;

        // Make sure that we’re using a full URL, not just the path.
        $url = UrlHelper::getSiteUrl($path);

        // For the sake of this example, we’re setting the $lastmod
        // value to the most recent time the location entry was
        // updated. You can pass any time using the DateTime class.
        $lastmod = $locationEntry->dateUpdated;

        // Add the URL to the sitemap
        craft()->sitemap->addUrl($url, $lastmod, Sitemap_ChangeFrequency::Daily, 0.5);
    }
}

$loc = UrlHelper::getSiteUrl('special/route');
$lastmod = new DateTime('now');
craft()->sitemap->addUrl($loc, $lastmod, Sitemap_ChangeFrequency::Yearly, 0.1);

$element = craft()->elements->getElementById(2);
craft()->sitemap->addElement($element, Sitemap_ChangeFrequency::Daily, 1.0);

$section = craft()->sections->getSectionByHandle('homepage');
craft()->sitemap->addSection($section, Sitemap_ChangeFrequency::Weekly, 1.0);

$group = craft()->categories->getGroupByHandle('news');
craft()->sitemap->addCategoryGroup($group);

echo $element->url;
// http://example.com/en/hello-world

echo craft()->sitemap->getElementUrlForLocale($element, 'fr');
// http://example.com/fr/bonjour-monde

echo UrlHelper::getSiteUrl('foo/bar');
// http://example.com/en/foo/bar

echo craft()->sitemap->getUrlForLocale('foo/bar', 'fr');
// http://example.com/fr/foo/bar

Sitemap_ChangeFrequency::Always
Sitemap_ChangeFrequency::Hourly
Sitemap_ChangeFrequency::Daily
Sitemap_ChangeFrequency::Weekly
Sitemap_ChangeFrequency::Monthly
Sitemap_ChangeFrequency::Yearly
Sitemap_ChangeFrequency::Never