This function will create a new list 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 list. Note that if you try and access a value in the list before it has been populated - i.e. the list is "empty" - then the return value may be 0 since internally the first few entries in the list are set when created to minimize performance issues when initially adding items to the list (although the ds_list_size() function will still return 0 on a newly created list). If you wish to ensure that the list is "truly" empty on create, then you should call ds_list_clear() after creating the list, which will then mean that any values returned for unpopulated list slots will be undefined.
list = ds_list_create();
This will create a new list and assign its index id to the instance variable "list".