Some times it's required to create folder inside the /uploads/ directory of WordPress. WP Codex function wp_mkdir_p() comes to rescue you. Let's say you want to create a folder StarLite inside the /uploads/ directory then below is code:
$your_folder_name = 'StarLite';
$upload_dir = wp_upload_dir();
$your_folder = $upload_dir['basedir'] . '/' . $your_folder_name;
if(!file_exists($your_folder)) wp_mkdir_p($your_folder);