They have excellent instructions and examples. I am setting up a free membership site. I have not looked at the capabilities for paid subscriptions.
Use 2 Browsers to set up. Stayed logged on as administrator to make changes to s2Message on 1. Use clear cache after making changes. Use another browser where you are not logged on as administrator to test. Goto http://cookdotcom.com and click membership to see a live example of how to sign up.
You can manage users from the dashboard using the native WordPress user tab. s2Message takes advantage of the builtin in roles and capabilities capabilities of WordPress and extends them!