What can heap store and stack........?

As Suthish says, I'm sure this question must have been answered before on this forum. However, briefly, the position is as follows:

In .NET, arrays are always stored on the heap. The elements are stored contiguously (i.e. one after the other) in memory and are preceded by information on the underlying type, number of dimensions and their sizes in a compressed format.

In the case of an array of value types (int, double etc), the elements contain the values themselves.

In the case of an array of reference types (string, object etc), the elements contain references (i.e. pointers) to where the objects themselves are stored elsewhere on the heap.

A variable containing a reference to an array will be stored on the stack if it's a local variable, a parameter passed by value or is an instance field of a value type which is itself stored on the stack. Otherwise it will be stored on the heap. 

In practice, it's not necessary to worry about any of this unless you're using unsafe code to access an array using pointers.