First you will want to set up your Email sending profile ,as this is where the info for the signature will populate from.
You will be able to enter logos and an image , as well as all your personal info you might want to populate, including your social media links. ( Enter the usernames only, no url as this is auto populated). Then go back to the signature creator and you can create signatures based on your emailing needs.
Once this is all set up, you can then go to your emails and phonescripts and create or edit emails and use the Pencil icon to add a signature that you have created.
You will not see the signature in the editing screen, but it will be available in the preview.