To use mCent, you need a smartphone. You also need to be in one of the participating countries, such as the United States, Argentina, Mexico, Vietnam, Russia, Sri Lanka, etc.
One of the drawbacks of mCent is that the app monitors your use of the apps, and it can freely access your address book. Of course, the app notifies you before doing anything, but that doesn't make it any less invasive.
mCent is an interesting app you can use to earn some money by simply downloading and opening certain apps.