Catalog Category

function getSomeRandomCategory(&$categories, $targetLevel, $currentLevel = 0) {
    if (count($categories)==0) {
        return false;
    }
    if ($targetLevel == $currentLevel) {
        return $categories[array_rand($categories)];
    } else {
        return getSomeRandomCategory($categories[array_rand($categories)]['children'], $targetLevel + 1);
    }
}

$proxy = new SoapClient('http://magentohost/api/soap/?wsdl');
$sessionId = $proxy->login('apiUser', 'apiKey');
$allCategories = $proxy->call($sessionId, 'category.tree'); // Get all categories.

// select random category from tree
while (($selectedCategory = getSomeRandomCategory($allCategories, 3)) === false) {}

// create new category
$newCategoryId = $proxy->call(
    $sessionId,
    'category.create',
    array(
        $selectedCategory['category_id'],
         array(
                'name'=>'Newopenerp',
                'is_active'=>1,
                'include_in_menu'=>2,
                'available_sort_by'=>'position',
                'default_sort_by'=>'position'
               )
    )
);

$newData = array('is_active'=>1);
// update created category on German store view
$proxy->call($sessionId, 'category.update', array($newCategoryId, $newData, 'german'));

$firstLevel = $proxy->call($sessionId, 'category.level', array(null, 'german', $selectedCategory['category_id']));

var_dump($firstLevel);

// If you wish remove category, uncomment next line
//$proxy->call($sessionId, 'category.delete', $newCategoryId);

$proxy = new SoapClient('http://magentohost/api/soap/?wsdl');
$sessionId = $proxy->login('apiUser', 'apiKey');

$categoryId = 5; // Put here your category id
$storeId = 1; // You can add store level

$assignedProducts = $proxy->call($sessionId, 'category.assignedProducts', array($categoryId, $storeId));
var_dump($assignedProducts); // Will output assigned products.

// Assign product
$proxy->call($sessionId, 'category.assignProduct', array($categoryId, 'someProductSku', 5));

// Update product assignment position
$proxy->call($sessionId, 'category.updateProduct', array($categoryId, 'someProductSku', 25));

// Remove product assignment
$proxy->call($sessionId, 'category.removeProduct', array($categoryId, 'someProductSku'));