Working with Sites (Multisite)

You can create subsites in pimcore very easily directly in the context menu: 

That's basically all, everything else is done in your code. 

Code Snippets (since 1.4.3)

Check if current request is inside a subsite

if(Site::isSiteRequest()) { /* ... */ }

Working with the navigation helper

See Navigation (since pimcore 1.4.0)

Getting the full path of a document inside a subsite-request

$document->getRealFullpath(); // returns the path including the site-root
$document->getFullPath(); // returns the path relative to the site-root

Getting the root-document of the current site

if(Site::isSiteRequest()) {
    $site = Site::getCurrentSite();
    $navStartNode = $site->getRootDocument();
} else {
    $navStartNode = Document::getById(1);
}