From the Joomla! Certification website:
The Joomla! Administrator Exam is the first available Joomla! certification exam. It covers topics related to the everyday use of building, managing and maintaining Joomla! websites.
The Administrator Exam is part of the Joomla! Certification Program. Its goals are to establish a certain standard and provide a documented measurement of knowledge. This ensures the competence of Joomla! professionals and contributes to the development of a qualified workforce. It will also provide clients an easier way to find a Joomla! Professional.
The Joomla! Administrator Exam is based on a clean Joomla! installation (downloaded from joomla.org) using the default language (en-GB), the default editor (TinyMCE), default template (Protostar) and settings, without any 3rd party extension or customisation.
To study for the exam, you can visit the Learning Guide and also attend the Exam Review.