The European Patent Office (EPO) has published the ‘European Patent Register: an introductory guide’, a publication where you can find all the information you need to start using this service.

The European Patent Register contains the publicly available information on the patent applications that the EPO manages. The information includes the status of the patent application as well as public documents related to, for example, oppositions and written communications between patent attorneys and the EPO.

Source
European Patent Office (EPO), www.epo.org