Dark Raider,
You need to give people time to respond to your questions.
We don't hang out here all day waiting for people to ask questions, just so we can answer them. :lol:
Now, that said, you'll find that the seats are typcially more comfortable than those you'd find in an airplane.
The quiet car is a car on certain trains where you cannot use your cell phone, in fact it must be turned off. You also cannot use laptops or other things that make noise, and conversation should be kept to a minimum and only then at very soft levels. The idea is that some people want to take a nap in this car.
As for dining cars, you won't see any on your trip between Boston and New York. They only run on trains that are going long distances and typically run overnight. However, to answer the question, anyone on the train can use the dining car if there is one. It is not restricted to class. People in First Class however do get to take their meals in the car for free, while those in coach must pay for the meal.
On your trip, you'll only see a cafe car. This car typically does have tables to eat at, but they don't come with table cloths, silverware, flowers and things like that. There are also no waiters in the cafe car, you buy your own food at the counter and carry it to the table yourself.
Ps. I've deleted the other topic that you created about the dining car, since you had already asked the same question here.