Before you use clan, you’re going to need to setup your access to the Google Analytics API. Follow the instructions in Google’s docs to register an application and create the client_secrets.json file.
Once you’ve got a client_secrets.json file, clan will walk you through acquiring an oAuth token:
By default this token will be named analytics.dat. I suggest you move this file to ~/.clan_auth.dat. clan will always look for the auth in that location so you will only need one copy no matter what directory you are running clan from.