In addition to stefgosselin's answer that has some mistakes: Lets start with his array:

$input = array(1,2,3);

This contains:

array(3) {
    [0]=> int(1)
    [1]=> int(2)
    [2]=> int(3)
}

Then you do array_slice:

var_dump(array_slice($input, 1));

The function will return the values after the first element (thats what the second argument, the offset means). But notice the keys!

array(2) {
    [0]=> int(2)
    [1]=> int(3)
}

Keep in mind that keys aren't preserved, until you pass true for the fourth preserve_keys parameter. Also because there is another length parameter before this, you have to pass NULL if you want to return everything after the offset, but with the keys preserved.

var_dump(array_slice($input, 1, NULL, true));

That will return what stefgosselin (incorrectly) wrote initially.

array(2) {
    [1]=> int(2)
    [2]=> int(3)
}