"Warning: mkdir() [function.mkdir]: Permission denied in" I'm new with PHP

if ( ! defined( 'ABSPATH' ) ) {
    exit;
}

if ( ! class_exists( 'Redux_Filesystem' ) ) {
    class Redux_Filesystem {
        private $parent = null;

        public $fs_object = null;

        public function __construct( $parent ) {
            $parent->filesystem = $this;
            $this->parent       = $parent;
            add_action( 'all_admin_notices', array( $this, 'ftp_form' ) );
        }

        public function ftp_form() {
            if ( isset( $this->ftp_form ) && ! empty( $this->ftp_form ) ) {
                echo '<div class="wrap"><div class="error"><p>';
                echo __( 'Unable to create a required directory. Please ensure that', 'redux-framework' );
                echo ' <code>' . Redux_Helpers::cleanFilePath( trailingslashit( WP_CONTENT_DIR ) ) . '/uploads/</code> ';
                echo __( 'has the proper read/write permissions or enter your FTP information below.', 'redux-framework' );
                echo '</p></div><h2></h2>' . $this->ftp_form . '</div>';
            }
        }

        public function execute( $action, $file = '', $params = '' ) {

            if ( ! empty ( $params ) ) {
                extract( $params );
            }

            // Setup the filesystem with creds
            require_once( ABSPATH . '/wp-admin/includes/template.php' );
            require_once( ABSPATH . '/wp-admin/includes/file.php' );

            if ( $this->parent->args['menu_type'] == 'submenu' ) {
                $page_parent = $this->parent->args['page_parent'];
                $base        = $page_parent . '?page=' . $this->parent->args['page_slug'];
            } else {
                $base = 'admin.php?page=' . $this->parent->args['page_slug'];
            }

            $url = wp_nonce_url( $base );

            if ( ! isset( $this->creds ) ) {
                if ( false === ( $this->creds = request_filesystem_credentials( $url, 'direct', false, false ) ) ) {
                    $res = $this->do_action( $action, $file, $params );
                    if ( $res ) {
                        $this->creds = true;
                    } else {
                        return true;
                    }
                }
            }

            if ( ! WP_Filesystem( $this->creds ) ) {

                $res = $this->do_action( $action, $file, $params );
                if ( $res ) {
                    return $res;
                } else if ( is_admin() ) {
                    // our credentials were no good, ask the user for them again
                    ob_start();
                    request_filesystem_credentials( $url, '', true, false );
                    $this->ftp_form = ob_get_contents();
                    ob_end_clean();

                    return true;
                } else {
                    return false;
                }

            }

            return $this->do_action( $action, $file, $params );
        }

        public function do_action( $action, $file = '', $params = '' ) {

            if ( ! empty ( $params ) ) {
                extract( $params );
            }

            global $wp_filesystem;

            if ( defined( 'FS_CHMOD_FILE' ) ) {
                $chmod = FS_CHMOD_FILE;
            }

            // Do unique stuff
            if ( $action == 'mkdir' && ! isset( $this->filesystem->killswitch ) ) {
                wp_mkdir_p( $file );

                $res = file_exists( $file );
                if ( defined( 'FS_CHMOD_DIR' ) ) {
                    $chmod = FS_CHMOD_DIR;
                } else {
                    $chmod = 0755;
                }
                if ( ! $res ) {
                    mkdir( $file, $chmod, true );    /** THIS IS LINE 104 **/
                    $res = file_exists( $file );
                }
            } elseif ( $action == 'copy' && ! isset( $this->filesystem->killswitch ) ) {
                $res = $wp_filesystem->copy( $file, $destination, $overwrite, $chmod );
                if ( ! $res ) {
                    $res = copy( $file, $destination );
                    if ( $res ) {
                        chmod( $destination, $chmod );
                    }
                }
            } elseif ( $action == 'put_contents' && ! isset( $this->filesystem->killswitch ) ) {
                $res = $wp_filesystem->put_contents( $file, $content, $chmod );
                if ( ! $res ) {
                    $res = file_put_contents( $file, $content );
                    if ( $res ) {
                        chmod( $file, $chmod );
                    }
                }
            } elseif ( $action == 'get_contents' ) {
                $res = $wp_filesystem->get_contents( $file );
                if ( ! $res ) {
                    $res = file_get_contents( $file );
                }
            } elseif ( $action == 'object' ) {
                $res = $wp_filesystem;
            }
            if ( isset( $res ) && ! $res ) {
                $this->killswitch = true;
            }

            return $res;
        }
    }
}