I was just trying to add a group, which is a very easy thing to do in Linux, especially when using GUI.
But it turned out that it is such a pain to do so with Mac OS X. Maybe it's because I'm new to it and not familiar with it. But I wonder if it is because of OS X or FreeBSD.
Also I found that copying and pasting an application on Desktop actually copies the entire application to the Desktop folder instead of creating a short cut on it like in Linux. So I opened a terminal window and created symbolic link inside the Desktop folder. But I wonder if general Mac users would do that or even know what symbolic link is.
It seems that I have a lot to learn. Despite of it, I'm enjoying using Mac. It's just that so far, Ubuntu is much easier to use for me.