You can take a train or bus around the Disneyland park by just stoping by the Main Street Transportation Co. Here you can see some old fire engines and trucks and get on one of the transports that will take you to each of the lands of the park.
Each of them are hop-on hop-off so there is no extra cost.
From Paris take the RER (commuter train) Line A direction Marne-la-Vallée. A station in central Paris from where you can get it is Chatelet. It takes approximately 45 minutes to get to Disneyland from there.
Get the Paddy wagon stationed in front of the "Main street". It will bring you to the main attractions of this Disney World.