ARX is just another file format. It is designed to contain an arbitrary amount of data chunks in a compressed state. Additionally the data chunks may be named, typed, versioned and structured in a directory tree. It therefore very much resembles any form of tar.bz2, tar.gz, rar or zip with the files beeing the data chunks.
From a pragmatic point of view this very much covers the functionality but I wouldn't have done this library if it didn't provide at least some advantage or additional feature.
To start reading and learning about libarxx you could start with Arxx::Archive which is the entry point for almost every Arxx session. Also the Arxx::Item is very important. Additionally the Modules page is recommended for reading.