In brief,

Heap

1. Any instance/member variables are stored in heap
2. created java object is in heap, no matter it is created in a method or not

Stack

1. stack stores local primitive variables
2. stores the local reference variable which points to object of heap
3. last in first out

Example

public void test() {
    
    int i = 1;
    Student s = new Student();
}

For above code, int i = 1 is stored in stack, Student s = new Student() will create a Student object in the heap, and there is local reference variable s in stack.

References

Please refer to following links for more detail:

journaldev

decodejava

jenkov