Displaying site description (tagline) and increasing the secondary menu's size

Hey Patrick,

Thanks for contacting us!

1- You add following code to bottom of Functions.php file of your child theme (https://kriesi.at/documentation/enfold/child-theme/)

function av_get_site_desc() {
	$site_description = get_bloginfo( 'description' );
	return $site_description; 
}
add_shortcode( 'site_desc', 'av_get_site_desc' );

and use [site_desc] shortcode to display it wherever you want. To display it in header area, you can refer to this post – https://kriesi.at/documentation/enfold/header/#adding-a-header-widget-area and add a widget area to your header.
If that does not help, please post a screenshot showing the changes you would like to make. You can upload your screenshots on imgur.com and post the links here :)

2- Please add following code to Quick CSS field in Enfold theme options > General Styling tab

#avia2-menu a {
    font-size: 17px;
}
#top .social_bookmarks li a {
    font-size: 20px;
}

Best regards,
Yigit