Once you have connected your Xero account, to post a member into Xero, view the member in question.
Click on the orange tab at the top right, then click the "Post to Xero" button. If a member is already in Xero, the tab will be green, and the button will say "Update in Xero" with an extra button saying "View in Xero" that when clicked, will take you to that member (Contact) in Xero.