To connect your Fitbit to World Walking via our website click on Settings and then click on Apps on the menu that appears.
When you connect your Fitbit account to World Walking, we automatically bank your daily steps total after each day, allowing you to spend this on any of your solo or group walks.
Fitbit aggregates your daily steps and sends us the value in meters, which we store in our database. When you view your recent activity on World Walking, we convert those banked meters into steps using a standard conversion ratio, however this may differ from Fitbit's conversion and therefore the steps shown may look different.
To confirm that the kilometers have indeed been carried across correctly, login to fitbit.com and visit the "Log" page and click on "Activities". You can change the day shown in the graph using the left and right arrows just above, so click on the left arrow to select yesterday or two days ago. Underneath the graph, the steps and kilometers totals for your Fitbit account are shown. The kilometers value should match up with your recent activity on World Walking - just hover over the steps to see the equivalent kilometers and miles.
PS. You can change your details bank distance by visiting Settings > General on World Walking and changing the "Unit" dropdown.