Dougie's summary is admirable, but I think that you need to know a bit more to bring it into focus, in spite of Douggie's final comment!
The European Aviation Safety Agency EASA produces Regulations that are in force in all EU States (27).
These Regulations cover Airworthiness, Flight Standards, Air Traffic Management and Air Navigation Systems and, soon, Aerodromes.
Under each of these headings, EASA issues Implementing Regulations. Airworthiness has 2, Initial Airworthiness and Continuing Airworthiness.
You are interested in the
Implementing Regulation for Continuing Airworthiness, referred to as EC 2042/2003. An-up-to-date ("Consolidated") version of this is available,
click here. This document has the information you need. (Well, you also need AMCs and GM, but we won't go there at the moment!)
EC 2042/2003 has 4 "Parts".
Part M Part 145
Part 66
Part 147
Part M tells you the
requirements for maintenance that aircraft operators and owners are responsible for. As such you need to know about it.
Part 145 tells you
how the maintenance is to be carried out.
It helps to understand this if you think of a car owner; it's her legal responsibility to make sure the annual road-worthiness certificate is current. That's Part M. The approved garage has the Government's rules for inspection, repair and issue of the certificate. That's Part 145.
The other Parts deal with licensing and training, as you know from Douggie.