gistfile1.txt

function add_addthisevent() { //make a function
    wp_enqueue_script( 'add_this_event', //name it 
                       'https://addthisevent.com/libs/1.5.8/ate.min.js', //point to the script you want to enqueue
                       '1.5.8', //what version is the script
                       true); //true puts it in the footer and false puts it in the header
}
add_action( 'wp_enqueue_scripts', 'add_addthisevent' );