This function will create a new stack data-structure and return the index value. This value should be stored in a variable and used in all further function calls relating to the stack.IMPORTANT! When you create a data structure, the index value to identify it is an integer value starting at 0. This means that data structures of different types can have the same index value, so if in doubt you should be using the ds_exists function before accessing them. Also note that indices are re-used, so a destroyed data structure index value may be used by a newly created one afterwards.
stack = ds_stack_create();
This will create a new stack and assign its index id to the instance variable "stack".