Does the Apple watch 3 do all the same things as a Fitbit charge 3?
Yes, the Watch will do all of that or more. Be advised the goals of the Fitbit are devised around steps taken and can do things like showing you that for the last month you have walked to Moscow or such. The Watch does track your steps but downplays them concentrating more on calories burned. Apple Watch Series 4 - Apple
The two devices probably have very different functions. Checkout https://www.apple.com/watch to see details of what the current Apple Watch can do for you.
Since most people here don't have a FitBit Charge 3 you would need to list what these functions are.
It very likely does more. Though it may do some things differently.
What functions from the Fitbit are you looking for exactly?
Here's the website with all the information on the Fitbit charge 3.
Everything a Fitbit charge 3 does.
Apple watch 3
