Java multiple classes

http://www.youtube.com/watch?v=XqTg2buXS5o&feature=player_profilepage#t=179s

     tuna tunaObject = new tuna();


Someone care to explain why you need to type "tuna" at the beginning and "tuna()" at the end if you already stated that you're going to use the tuna class at the beggining?
I think I understand the "tunaObject" is(the variable to which you will assign the new class in the main class, right?), but the "new" is still kind of ... I don't understand it either...
:/

>>30
So when you make a class it becomes a new data type itself which you use to declare new variables?
Does that mean there are classes for String, double, int, etc?

That's what doesn't make sense to me.