The Social Media Settings menu allows you to customize the default post message when a constituent clicks on one of the social network buttons. You can find the Social Media Settings menu by clicking in the left-hand menu from the keyword you want to change the share settings. You will be able to customize the share message for Facebook and Twitter posts, text messages, and emails (text and email only available in Crowdfunding).
In a Crowdfunding keyword, the Social Media buttons share the fundraising page you are currently viewing. In a Text to Donate/Event/Ticketing keyword & form, the Social Media buttons are on the Thank You page, after you've donated or bought tickets, to share the form to their friends and family.
Write your share messages from the perspective of the supporter or donor by using first person pronouns like I and My. Remember that the volunteer fundraisers and donors will be the ones sharing, so write it as if they did it themselves. This will easily provide your volunteers with marketing material to use in their fundraising efforts.