The core of gamification can be boiled down to two key components. Goals and Feedback. Of course, there is more going on that supports these, but those are the two keys of gamification.
Gamified systems need to set specific tasks for users to complete, and then provide them with feedback as they progress towards completing those tasks. A good gamified system then uses other techniques, elements, mechanics etc to support the user towards those goals.
The hard bit is setting good goals, creating good feedback mechanisms and wrapping the experience in something that is engaging! But that is for later.