Mid30sLife – You can add other social media icons to your menu by following the instructions on the theme info page:
https://theme.wordpress.com/themes/sorbet/
You can add links to a multitude of social services to a toggle menu (the heart icon) by following these steps:
– Create a new Custom Menu, and assign it to the Social Links Menu location
– Add links to each of your social services using the Links panel
– Icons for your social links will automatically appear under the heart icon in the header
It looks like you set up your custom menu, but so far you’ve only added Facebook there. Just go to Appearance > Menus, select your Share menu, and add Twitter and any other links you’d like.
It looks like your site is on WordPress.com, so the best place to get further help is in the support forums that stephencottontail linked to above: https://en.support.wordpress.com/
This forum is for folks who install WordPress on their own servers. Good luck!