# puts folder A into folder B
rsync -avuc --delete "/home/user/A" "/home/user/B"
 
# puts contents of folder A to folder B
rsync -avuc --delete "/home/user/A/" "/home/user/B"

-a       - do the sync preserving all filesystem attributes
-v       - run verbosely
-u       - only copy files with a newer modification time (or size difference if the times are equal)
-c       - checksum both folders before transferring for cases where above fails
--delete - delete the files in target folder that do not exist in the source