Each candidate to EU competitions needs to register in two ways: you need to create an online account on EPSO's website in which you provide information about yourself, your qualifications, language knowledge and other relevant information. Secondly, you need to apply for a specific exam that is currently open.
All this information is shown in your EPSO account (or profile) so you can consult it at any moment, update contact information if needed and this is where EU institutions take the information from when they need it.
See also:
EPSO Address, EU Institutions, EU Recruitment Exam
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