Find all directories (type d) up to a maximum depth of 4 (maxdepth 4) in the root directory (/) that are not hidden ( ! -path '*/\.*' ) and execute the command du -h (disk usage in human readable format) on each of them ( -exec du -h {} \+ ) and sort the results by size (sort -n -r).
find / -maxdepth 4 -type d \( ! -path '*/\.*' \) -exec du -h {} \+ | sort -n -r