This WordPress plugin allows you to highlight text and share it via Twitter and Facebook.
To install this plugin go to your WordPress Dashboard then go to Plugins > Add New. Type in Highlight and Share.
Select Install Now and Activate the plugin. Once activated you will find it under Settings > Highlight and Share.
When you are on the setup page you can enable and disable Twitter and Facebook. Type in your Twitter username (without the @ symbol) and more. Once complete select Save Changes and you will then see this below when text is highlighted on your websites.