Usage is pretty straight forward.
This is some example code:
$page = \Page::getCurrentPage(); //get attribute $page_selector = $page->getCollectionAttributeValue('page_selector_handle'); //if there is a page selected if($page_selector > 0) { //get the page object by id $npage = \Page::getByID($page_selector); //if its a valid page if(is_object($npage) && !$npage->isError()) { //get the path $page_target = $npage->getcollectionpath(); } }