I can see how to specify the source to sync. What I cannot see (or figure out) is how to specify that the source on system A C:\Users\Bob\Documents\school should sync with the target on system B D:\school, and visa-versa.
You first add the folder on some device (A or B doesn’t matter). There you pick whatever path you like. For simplicity, imagine you choose A.
Then you share that folder with device B. Device B should now give you a popup “device A wants to share folder XY…”. When you click accept on that popup, you get a dialog pretty similar to the one you had when you initially added the folder. In this dialog you can also enter a path - enter the path for device B here.
In case you have auto-accept on (can be set per-device in the device settings), you never get the popups and folders are added automatically in the default location.