create a file called theme--settings.php inside the theme folder in sites/all/theme we use the hook
theme_form_system_theme_settings_alter to add a settings for to default settings page
theme_form_system_theme_settings_alter to add a settings for to default settings page
function hithin_form_system_theme_settings_alter(&$form, $form_state) { $form["socialmedia"]=array
( "#type"=>"fieldset",
"#title"=>t("Socialmedia"),
"#collapsible"=>TRUE,
"#collapsed"=>TRUE
); }
read formapi for further details of the form