Yes, the train station is very convenient. Just get on an RER A train that has the "Disneyland Parc" stop lit up on it. You will also need a ticket for the outer regions, as Disneyland isn't in the "city center", so the ticket is a few more euros than a standard subway ride. Depending how much you will be riding the subway, you might looks into a Paris Visite card for unlimited metro/bus rides for designated number of days. Also, it gets you discounts at museums and disneyland tickets. Hotels in Paris also regularly have tickets for sale, so if you want to save a few euros, shop around to see what the best deal is.
Oh, and one more thing -- I don't know how good your French is, but don't be nervous at all about that in the park... Everyone is very helpful in whatever language you need (it would seem)!!!