Correct. You do not enter Fitbit data into MFP. It gets added (as needed and if needed) when you connect to the Fitbit base station. I keep mine at home, so my data gets uploaded at the end of the day when I get home from work. Today I got 217 extra calories for my walk. They would normally count toward my "activity calories"--those extra calories MFP gives you when you exercise, but I ignore that part of MFP.
"Fitbit adjustment" is a figure brought automatically into MFP from Fitbit. This is what MFP says about it:
"When the data reported by your Fitbit shows that your actual calories burned and your estimated calories burned for the remainder of the day are higher than our original estimate for the entire day, we'll adjust your net calorie goal accordingly. The "Fitbit Adjustment" represents the additional calories you have burned, above and beyond our original estimate. Because this value is recalculated every time your FitBIt uploads new data, you should expect this value to change over the course of the day."
It's really neat the way it all works together and I do like it. At the same time, it can be pretty confusing. There's a forum on Fitbit.com for users who integrate with MFP, and Fitbit customer support is pretty helpful with questions if you have any.
There are things I wish both web services did differently but as they are, I still get more information out of them than I would have otherwise.
Hopefully this helps rather than confusing more! :)
4'11" tall * 46 years old * Attitudes are contagious. Is yours worth catching? :)