hello marios.
firstly the loop is your full live feeds, which on a circuit go between one light fitting and the next to bring power to each room..
secondly if you are unsure of what yoare u are doing don't do it. get an electrician in.
the 3 cables will be
loop in power in to this room. loop out power on to next room. and switch wire. the brown cores from the loops are connected together with the brown from the switch wire in a connector. NOT connected to the light fitting .the the blue from the switch wire will then connect into the L of the light. As this will now become a live wire this must be identified as one. it should have some brown sleeving on it (when you disconnect the old light make a note of this core). and the other two blue cores will be the neutral cores and will connect in the N Terminal. I do hope that you are confident enough to perform this job and always remember that you cant see it. Smell it, or hear it, but electricity can kill you.. be safe
michael
July 2008