The journey between Paris and Disneyland Resort, Paris takes around 35mins. The trains have plenty of capacity, and are sometimes two storeys in height. RER trains can be a little daunting for foreign visitors, but relax, you should be fine!
The RER service is met by numerous Metro routes along is route, so connections to other parts of the Paris region are easy.
Paris RER System
Paris' RER system crosses the city, linking its suburbs to allow for faster connections across the city. There are five lines in total, each with their own branch lines. RER trains are less frequent than Metros, and are effectively a suburban train network (but underground in central Paris).
RER stations are marked by white and blue signposts, and each line can be identified by its colour and number.