How do i activate authenticator serial number?

[Dalapie-twisting-nether]

i recently came back and noticed that i have to setup an authenicator to make groups in groupfinder… now the issue is whenever i try it says inactive, and setting one up forces me to get a serial number and authenticator code, but i do not have that?? i get a 10 minute code to enter before to setup this but where do i get a serial number??