Create sidebar/widget area in WordPress

functions.php

function criaSidebars() {
  register_sidebar( array(
    'name'          => 'Sidebar Principal',
    'id'            => 'main-sidebar',
    'before_widget' => '<div>',
    'after_widget'  => '</div>',
    'before_title'  => '<h2 class="">',
    'after_title'   => '</h2>',
  ) );
}
add_action( 'widgets_init', 'criaSidebars' );