I have been using Ubuntu for quite some time now. But I haven't yet got the hang of it. One of the reasons is that due to the excellent support that the Ubuntu community offers, I find specific answers for the specific questions that I have and my Ubuntu system still runs pretty alright.

There are sections of my file system that I completely avoid (to avoid messing up the system files of my Ubuntu) and then there're are user folders like "Documents", "Downloads", etc. which I use the way I would have used them if I were using my Windows OS. 

Coming to my specific question: I wanted to install the plugin TeXlipse ([installation instructions][1]) and for that I am supposed to remove any previous version of it. Maybe the eclipse GUI is sufficient to achieve this end, but it compels me to ask a few more general questions:

 1. What's the equivalent of "add or remove programs" in Ubuntu?
 2. Is there a good tutorial on user management (with good schematics for better understanding)? Currently since I am a single user, I first try a command. If it doesn't work I try it with "sudo" and then it usually works. But if you see the problem, I haven't really understood when I should use "sudo". Since I am the only admin and the only user, my approach almost always works, but I want a deeper insight.
 3. I have understood how to change the "PATH" variable on Ubuntu (using terminal), but is there a GUI (like the "system properties" in Windows) where I can do that?
 4. In Windows there're perhaps only a couple of important folders (by important I mean important in my logical picture of the Windows file system)  in the installation drive (in my case C:\). Namely "Program Files" and "Windows". I simply stay away from "Windows" folder and the "add remove program files" is good enough to handle the "program files" folder of Windows. Of course there's a folder named "Users" where the users (who are not admins) can access only their folders. 

Thus there's a clear picture at some level in my mind of the Windows file system. In Ubuntu, when I reach the location "/", there's a huge list of folders, most of which I have no clue as to what they contain. The "/bin" folder seems to be the equivalent of the "Windows" folder in windows. The "/usr" folder seems like it's the equivalent of the "Users" folder in Windows. But even the "/home" folder looks like it can fit the bill.

Please understand that I do understand, that Ubuntu (Linux) has a different character than that of Windows, i.e., there need not be exact equivalent of Windows functions, in Ubuntu. All I am looking for is a bit more clearer picture of the Ubuntu file system.

  [1]: http://texlipse.sourceforge.net/manual/installation.html