When you set-up a new Castopod server, there no link or hint on how to sign-up from Castopod homepage.

That is not ideal, as it is not clear what to do next.

You cannot do anything for your podcast without being able to sign-in.

The actual sign-in page is at /cp-auth/login

So, for example, if you Castopod server is a https://example.com/ then the sign-in page would be at https://example.com/cp-auth/login