Complex sentence: The RER station is directly connected to Magenta station which was constructed further underground to the east of Gare du Nord in order to service RER E which connects Gare du Nord to Saint-Lazare/Gare Saint-Lazare.
Split into simpler sentences: The RER station is directly connected to Magenta station, which was constructed further underground to the east of the Gare du Nord. It is served by the RER E line that offers a link between the Gare du Nord and Saint-Lazare/Gare Saint-Lazare.