I want know what are things actually stores on heap and stack

the only things that are stored on the stack are local variables and parameters passed by value.

everything else is stored on the heap where local variables or value parameters refer to reference

types (such as string, object etc), only the reference is stored on the stack. The object itself

(unless the reference is null) is stored on the heap.

https://www.c-sharpcorner.com/article/C-Sharp-heaping-vs-stacking-in-net-part-i/

https://www.c-sharpcorner.com/article/stack-vs-heap-memory-c-sharp/#:~:text=Difference%20between%20Stack%20and%20Heap%20Memory%20in%20C%23,-Category&text=It%20is%20a%20LIFO%20(Last,and%20removed%20in%20any%20order.