Client Area Addons

I'm completely new to addon development so please forgive me if I'm missing something, but I'm a bit confused about a couple of things. I hope this makes sense.

I'd like to be able to allow users/clients to set configuration parameters (e.g. do some authentication with another service and I guess store a user-specific authentication token), but I can't figure out how to display content in the client area without having the user visit a specific URL.

Is this possible? Would I need the administrator to somehow update their UI to link to the aforementioned URL or can I do this within the module code?

Thanks.