How can I find out what is taking up space on my hard drive? I have a tiny hard drive - 128 GB. I am not that technical. I see that other files under storage is taking up say 40 GB of space. My boyfriend got me a WD NAS hard drive and I was able to move my photos from iPhoto, and iTunes, there to free up some space.
I accidentally deleted iPhoto so in order to install it.
My boyfriend showed me a script that showed the size of some big directories.

.3G   /Applications/iMovie 9.0.9/iMovie 9.0.9.app/Contents/Resources
1.3G  /Applications/iMovie 9.0.9/iMovie 9.0.9.app/Contents
1.3G  /Applications/iMovie 9.0.9/iMovie 9.0.9.app
1.3G  /Applications/iMovie 9.0.9
2.0G  /Applications/iMovie.app/Contents
2.0G  /Applications/iMovie.app
5.3G  /Applications/Install OS X Yosemite.app/Contents/SharedSupport
5.3G  /Applications/Install OS X Yosemite.app/Contents
5.3G  /Applications/Install OS X Yosemite.app
1.1G  /Applications/iPhoto.app/Contents/Resources
1.3G  /Applications/iPhoto.app/Contents
1.3G  /Applications/iPhoto.app
1.0G  /Applications/Microsoft Office 2011/Office
1.2G  /Applications/Microsoft Office 2011

Can i delete the iMovie directory and maybe download it at a later time?
Is there a better way to figure out where all the space is being taken up?
Like lets say I had an 18 GB zip file saved on my desktop. Theoretically that would be under the other space category but OS X isn't helping make me aware of that file. How do I find big files like that? Mind you i don't have a 18 GB zip file sitting around but I am trying to find if I have any big files sitting around to delete.
I highly recommend using:  http://daisydiskapp.com 

.. Once downloaded and installed they have a "Test Drive" option you click that lets you use it for free.  Please note that to see all files on your HD that all users own, you will want to use the "Scan as Administrator" option, which will prompt you to enter your password.

There is also:


Disk Inventory X - http://www.derlien.com
Disk Map - Google for "Disk Map OS X" ( Commercial software )