When you look at the documentation of split, you'll see that the regular expression is followed by a comma before the next argument.

my @items = split /:/ $line;

Assuming the quoted statement is made syntactically correct as haukex suggests, if you print or dump (see the Data::Dumper core module) the  @items array with
    print @items;
or
    use Data::Dumper;
    print Dumper \@items;
do you see what you expect?

If the  @items array contains what you expect, how would you access a specific element of the array (which would correspond to selecting a field of the original record)? How would you select multiple fields? Might it be more convenient to use an array slice?

You have a simple syntax error in your call of the built in split function.

use strict;
use warnings;

my $line = "This is :a line :with colons :in it";

my @items = split /:/, $line;

print "$_\n" foreach (@items);
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If you are working through Learning Perl, Chapter 9 explains some basic usage of split.

If you are like me and forget syntax easily, try to remember that things like split and print are built in functions of Perl and as such should be treated like any subroutine call where you wrote the subroutine (just no "&" ever necessary, see Chapter 4 of Learning Perl :-)). You can even wrap parenthesis around the list (list implies comma separators) of arguments you are passing them for clarity... e.g.

my @items = split(/:/, $line);

print('just ', 'like ', 'this ', ':-)')
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EDIT: Also, if you are only looking to extract certain items of your list for each line, and you know their index locations in the array you split them in to, you may want to take a look at array slices which are covered in Chapter 17 of Learning Perl.