Where are you using Fill & Sign? It is a website in the Document Cloud https://cloud.acrobat.com/fillsign, a tool in Acrobat/Reader DC, and an iOS app - which are you using?
Are you trying to create a new signature, or to sign a PDF? What happens when you try to create a new signature? A screen shot and detailed description would help.
PS - Tutorial which is for the web app in the Document Cloud, but most of it also applies to the Acrobat/Reader and iOS versions: Adobe Fill & Sign