External drives should be detected and prompt you to use them. Did you by chance click the option not to use a drive and not to ask about it later? If you said yes to use it and yes to use the lmce layout, you should see a /home/public/data/* filesystem structure where you can put your media. If that's the videos folder you are talking about, and answered yes to use the drive, then the only other thing I can think of is you may have turned off the update media daemon.