The Just Dance Now is a separate mobile game you can play with your smartphone and your TV. You don't need to have the Just Dance game in order to play the Just Dance Now.
The Just Dance Controller App is needed to play the PC version of the Just Dance 2017. It is also an option for console instead of using the Xbox One with Kinect, PS Move, PlayStation Camera with DualShock 4 or the Wii Remote with WiiU GamePad.
For Xbox360 you will need the 360 Gamepad and Kinect.
For PS3 you will need PSMove and the PlayStation Eye.
For Wii you will need the Wii Remote but you can also use a microphone for karaoke scoring.
If you would like to know more about other features of Just Dance 2017, check out our related FAQ.