Habitats are the "buildings" where your dragons are stationed. Each habitat has a certain earning per hour, and a maximum amount that can be stationed at a time. You will need to collect gold from the habitats. Fastest way to get this is by building more habitats and upgrading them (with the gold you get). This will increase the amount of gold the habitats generate. As an indication, I got this at the time that I was level 11, and had about 5 habitats. If you're going for the full completion of this game, this achievement will come naturally.
- You can see your progress for this achievement(and also for others) when you select the "trophy symbol" on the right side of your screen. Not the green one that takes you to the XBL achievements, but the other one.