The Samsung Galaxy Note 4 has problems similar to other Samsung models like the Galaxy S6 Edge where it doesn't connect well with the Fitbit Charge or Fitbit Charge HR. Installing the Fitbit App from Google Play is easy enough.
If you already have a Fitbit account where you have registered your Charge HR, the same Charge HR will show up in the Fitbit App.
After you select the Charge HR, if you haven't already turned on Bluetooth on your Galaxy Note 4, you will see a warning that Bluetooth is off.
It's pretty easy to turn on Bluetooth on the Note 4 by sliding your finger down from the top of the screen to open up the quick settings options, and pressing the Bluetooth icon.
Unfortunately, despite the great pairing potential between the Fitbit Charge HR and the Galaxy Note 4, the Fitbit App is unable to connect to the Note 4 over Bluetooth giving an exclamation point warning in a red circle. The cynic would say that Samsung is trying to promote its own fitness products like the Gear Fit. Regardless, it's a real shame that two of the most popular products in the smartphone and wearables category don't work with each other.