While you are able to gain experience, you are also able to lose HP by participating in bad habits, or failing to complete one of your dailies. If you have a habit that you want to lose, like saying "I'm Sorry" all the time, or eating junk food, you can add it as a negative in your habits. When you participate in that activity, you can then select it in your dashboard of HabitRPG and it will deduct points from your health.
Along with each activity that you complete, you get in game money that you can use to buy new gear, health potions and other rewards that you can list out yourself. For example, if you are trying to play less video games and write more, you could have "two hours of video games" be a reward that you are able to purchase.
While I know that this sounds a bit pedantic and simple, this game has really helped me revolutionize my time, set goals, and enjoy the whole process. I enjoy the idea of being able to have a "Party" with my friends in which we motivate each other to do things, but I also like that we are all necessitated to do our dailies in order to complete the quests, and defeat bosses as a team. For example, if as a group we do not succeed in completing our dailies, the big boss that we are currently fighting against does not take as much damage, and it is possible that we won't be able to complete the quest.
Eventually, I think, the goal of HabitRPG is to be able to integrate with all kinds of self-tracking products, many of which I use already. They have a fully built out API, and a pretty strong and supportive developer community to help when you may be a bit lost. While this means that the feature set is not fully built out, it also means that there is a ton of room for potential growth—and that you can be a part of it. There's actually a great site here that elucidates some of the more complicated processes.
While I do think that HabitRPG has a long way to go, I appreciate it for its innovation and drawing together a number of my favorite apps into one easily consumable package. The community is very small, but growing rapidly—while there are only a few forums and other social activities available on the site, I can only imagine that they will grow as the game does. If you are a completionist, like I am, or even are just looking for a new, unique, productivity app—HabitRPG is probably for you.