I'm attaching a couple articles relating to the Fitbit from our Help Center.

How to connect your FitBit to Grokker:
https://support.grokker.com/hc/en-us/articles/360000423472-How-do-I-connect-my-Fitbit-or-Garmin-account-with-Grokker-

How FitBit works with Grokker:
https://support.grokker.com/hc/en-us/articles/360000432211-What-activities-from-my-FitBit-or-Garmin-are-synced-with-Grokker-

Where you can see your FitBit data on the Grokker website:
https://support.grokker.com/hc/en-us/articles/360000423512-Where-can-I-see-my-Apple-Health-Fitbit-or-Garmin-activities-on-Grokker-

What data does Grokker use from your FitBit:
https://support.grokker.com/hc/en-us/articles/360000423552-What-data-from-my-FitBit-or-Garmin-is-being-used-by-Grokker-

If you have any specific questions about how your Fitbit and Grokker work then shoot an email to customer support at support@grokker.com and I'm sure they'll be able to help you out!