In functions.php file, Add following code
add_action( ‘admin_menu’, ‘mycustompagemenu’ );
function mycustompagemenu(){
add_menu_page(
__( ‘My own Settings’, ‘textdomain’ ),
‘my theme settings’,
‘customize’,
‘mythemesettings’,
‘my_theme_settings_fun’,
get_template_directory_uri().’/images/icon.png’,
60
);
}
function my_theme_settings_fun(){
esc_html_e( ‘Admin Page’, ‘textdomain’ );
}
For more details