You can do this even without third-party software, using one of the windows built-in programs "xcopy" or "robocopy" (depends on wether you want to just fill directory B with new or changed files from A or you want a mirror copy of A, including the deletion of files, no longer present in A, on the remote end B).
Just create a .bat file with the corresponding command, and add that file to sheduled tasks, so it will be executed automatically every day/week/[whatever time you want].
Here is a quick example for an xcopy command (assuming "C:\directoryA" is the source and "\remote-pc\backup\directoryB" is the backup folder) :
xcopy /M /S /Y "C:\directoryA" "\\remote-pc\backup\directoryB"
Note that the remote folder has to be accessible in this way, that means you may have to setup a network share.