With the array shortcode you can build a static array to pass to other Shortcodes.
To use it, pass the elements of the array as arguments to the shortcode,
{array: 1 2 3}
will return the array
[1,2,3]
You can also use keyarg for associative arrays:
{array:@one=1 two=2 three=3}
will result in the array
['one' => 1, 'two' => 2, 'three' => 3]
There are many cases where this might be useful, but the most simple example of this is in combination with the Loop Shortcode, so that you can repeat a template many times for each element in a static list.
{loop:
{array: 27 109 356}
[{post:title}]
@sep=', '
}will print the title of the 3 posts with ID 27, 109 and 356, each separated by comma.