When I go to the hidden wiki page and go to a services site, I can't actually get things done and can't quite figure it out. The problem is that they want a username and password, but how do I register for that? There is no direction for that. Is it a secret word of mouth thing or do I have to search through forums or do I use my stack username and password?
Logging in to onionsites works the same way as logging into websites. Namely, it depends on the site. How do you log in to facebook? Well you have to sign up. How do you log in to gmail? Sign up with gmail. Every website has its own way of letter users sign up and log in. The same goes for onionsites. If you want a more specific answer, you need to provide a specific onion address.