MacOS – Newbie question on getting back hard drive space

I'm relatively new to Macs (PC guy) and my MacBook Air (1.8 GHz I5) running 10.9.1 OSX is reporting that the Startup disk is full. I'm trying to figure out what is taking up the room and how to clean it up somewhat. I am used to PCs and Windows Explorer where I can just start at the root folder, right click to look at size and drill down to the offending folder(s). I'm sure there is some straight forward way on the Mac. I've researched this problem somewhat and have already cleared out movies, music and photos. I've also run OmniDiskSweeper which clears up caches. All that cleanup only recovered 1 or 2 gigabytes.

I find it hard to believe the disk is full. I don't use it that often and I've only put a few things on (XCode, some GNU tools, Octave). I'd like to clean it up for other stuff. Under System info, the claim is that the disk is 121 GB flash, which is strange as I recall it being advertised as 160 but either I'm looking at the wrong place for the capacity or my memory is faulty. Under that same system info (click on apple->About this mac->More Info->Storage it appears that the vast majority of disk space is taken up by "Other", which isn't too helpful.

I am suspicious of the mail, but don't know how to check that. I'll post a separate thread (Question about Mai. How to limit amount stored locally. Where is mail stored?) for that as it's a stand alone question I'm interested in regardless of whether or not it is the culprit.

So in summary PLEASE tell me how to find out what is taking up the hard disk space and what I can clean off. An ability to browse the disk would be helpful. I'm somewhat comfortable with Unix/Linux on other system so I could do stuff by cmd line. But at least on windows/pc, if you start removing folders without doing an uninstall, you can have problems.

Thanks!

Dave