This thesis provides a general overview on how information technology supports the modernization of library systems, with a special focus on the role and importance of the free open source system for managing library Koha. Koha is an integrated system for library management that enables the automation of a wide range of library processes, including acquisition, inventory, cataloging, circulation, user management and reporting. The thesis was written from the perspective of a system librarian, a profession that arose in response to technological advances in libraries. The system librarian combines knowledge and skills in the field of informatics and librarianship and is crucial for the implementation and maintenance of library information systems. In order to understand how to operate within Koha system, the thesis deals with protocols and standards in library management and particularly emphasizes the importance of MARC standards and Z39.50 protocols, which enabled librarians to transfer catalogs into a machine-readable format and exchange information with other libraries. The thesis also reflects on the concept of free software, explaining the GPL license, one of the most famous and widely used licenses. The practical part of the thesis explains the example of installing Koha on a Linux virtual server, system configuration and importing data from another system. Based on this data, an example of writing SQL reports is presented. Through this thesis, we have established that library systems will continue to be developed in order to better adapt to the needs of users and librarians, and Koha is a desirable choice because it is an excellent system for managing library that can be adapted to different needs of users due to its freedom and openness.