The register_sidebar() function in wordpress https://code.recuweb.com/

register_sidebar.php

register_sidebar (array(

     'name'         => 'RightSideBar',
     'id'           => 'right-sidebar',
     'description'  => 'Widgets in this area will be shown on the right-hand side.',
     'before_widget'=> '<div id="%1$s" class="widget %2$s">',
     'after_widget' => '</div>',
     'before_title' => '<h3>',
     'after_title'  => '</h3>'

));