I am following a tutorial at https://www.youtube.com/watch?v=emT-CL957HE
Around 19:30, how does he turn off the array modifier for the duplicate? No matter what I do, they seem to share the same behaviour ie shadow the parent - can't figure out how he did it in the video.

Some other questions:

-What is the significance of Ctrl-L (at 18.30 and 20:00) and when is it used? I can't find any good info on the net that can provide a good example of the usage especially in the above context.
-What is the purpose of clicking Apply? Is there something that is irreversible once Apply is clicked?
Thanks in advance.