Hi there -- We have lots of helpful tips for connecting and sharing to your social profiles here in our Resource Center!
You can share a mailing directly from the "mailing success" page right after you've sent or scheduled a mailing. If you haven't connected your social profiles yet, you can do so from that page. You'll have the option to share to any profile or page that is linked to your login, and you can toggle between those accounts on the social connector page.
You can also share any past mailing directly from the Response page of your account: