What is the best way to access one array within an array?

De-reference it:

use strict;
use warnings;
use Data::Dumper;

my @aoa = ([0..3], [10..12]);   # array-of-arrays
print Dumper(\@aoa);

for my $aref (@aoa) {
    my @arr = @{ $aref };       # derefernce each array
    for (@arr) {print "$_\n"}   # access each scalar value
}

__END__

$VAR1 = [
          [
            0,
            1,
            2,
            3
          ],
          [
            10,
            11,
            12
          ]
        ];
0
1
2
3
10
11
12
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What is the best way to manipulate (add, modify, delete) a scalar value within an array?

Adding to left (push), adding to right (unshift), delete from left (shift), delete from right (pop), delete from middle (splice). See also perlfaq4, Data: Arrays.