The xtrabackup binary is a compiled C program that is linked with the InnoDB libraries and the standard MySQL client libraries. The InnoDB libraries provide functionality necessary to apply a log to data files, and the MySQL client libraries provide command-line option parsing, configuration file parsing, and so on to give the binary a familiar look and feel.
The tool runs in either --backup or --prepare mode, corresponding to the two main functions it performs. There are several variations on these functions to accomplish different tasks, and there are two less commonly used modes, --stats and --print-param.
For general inquiries, please send us your question and someone will contact you.