A ds_list is a data-structure that stores information sequentially as it is added (much like a 1D array). DS lists are very flexible data structures that permit you to add values at the end or insert them somewhere in the middle of the list, as well as giving you the ability to shuffle the order (to randomise the values) or sort them in an ascending or descending order.
When accessing DS list data structures, you should always try to use integer values for the list position, and all non-integer indices will be floored by GameMaker Studio 2 if you do not. If that is not what you require, then you will need to do the rounding yourself previously before passing the index that you wish to check.
The following functions exist that deal with DS lists.
Ds_lists can be used hold ds_maps and other ds_lists too, but only for use in conjunction with the json_encode function. This requires that you "flag" or "mark" the entry within the list so that it can be encoded correctly using the following special functions:
Apart from these specific functions you can all use an expression (called an accessor) to add or modify the contents of your ds_list. This accessor looks similar to a 1D array with the following syntax:
You can find more information, plus examples, from from the GML Overview page on Accessors.