This is the most confusing aspect of beginners trying to earn programming. It is the type of the data type.

Value types

Value types are stored on the stack. When assigning a variable from another, the value stored is copied. The data types that are value type are: bools, numbers, chars, strings, and all structs.

Strings are actually an immutable reference type, which makes it behave like a value type so it's more intuitive.

Example:

int x = 1; //the value of x is 1 and is stored on the stack
int y = x; //the value of y is the value of x. which is 1, and is also stored on the stack
y = 2; //the value of y becomes 2.
Console.WriteLine(x); //will output 1
Console.WriteLine(y); //will output 2

Reference types

Reference types are stored on the heap, and their address to them is in the variable on the stack. When assigning a variable from another, the address is the one that is copied. The data types that are reference type are... pretty much everything else that is not a value type... and that's classes. Will use collections to write an example (Note the snippet uses the for loop).

List<int> list1 = [1, 2]; //list1 holds a reference (stored on the stack) which points to the actual list on numbers (stored on the heap)
List<int> list2 = list1; //list2 copies the reference from list1. This means that it is pointing to the same list of numbers on the heap
list1[0] = 3;
list2[1] = 4;

//write list1. Will outout 34
for(int i=0; i<2; i++)
{
	Console.Write(list1[i]);
}

//write list2. Will also 34 since it is referencing the same list.
for(int i=0; i<2; i++)
{
	Console.Write(list2[i]);
}