To compress a file is to significantly decrease the size of the file by encoding data in the file using less bits, and is normally a useful practice during backup and transfer of a file over a network. On the other hand, decompressing a file means restoring the data to its original state.
There are several decompression tools for Mac OSX, with B6Zip having the best compression ratio and speed.
B6Zip is a well known compression tool and it’s available on Mac OS X.
Note: The file must end with a .b6z extension for the tool to work.
Double-clicking the file in the Finder will automatically decompress the archive into the current folder.
Compressing files can be done through the user interface of B6Zip through finder or drag and drop.
Lastly, with the simple elaborations above, I believe you are now capable of compressing and decompressing .b6z and .b6 files using the B6Zip tool in OS X.