Ten Things About Linux

(Note: I copied the following from http://www.handlewithlinux.com/things-you-need-to-know-about-Linux-coming-from-windows. For a discussion of the points made here, please follow the link and see the comments following the article.)

What you need to know about Linux if you're coming from Windows:

1. There is no registry in Linux

In Windows there is the registry, the registry is a database which keeps all your settings. If you want to change anything not in a menu (or in a menu) you need to use the regedit program. Or a script.
In Linux there is no such thing as a registry.

2. In Linux everything is a file

All configurations are in text files, and everything in Linux is treated as a file. This is a much simpler approach which makes it very easy to change things in Linux. In Linux even your filesystem itself can be viewed as a file.

3. In Linux there's no such thing as drive letters

In Linux all your "drives" are on the same tree, this means that instead of navigating to a drive letter you always navigate to a subdirectory.

4. You should see the command line as the registry editor

If you perceive the command line stuff in Linux as a difficult thing to cope with, remember the following:
The command line makes it possible to do everything (and a whole lot more) you would need to use regedit for in windows. The usual things are possible in the GUI, tweaking has to be done on the command line.
But you don't have to use the command line to change your garbage bin icon. You need regedit to do such a thing in windows. Think that's easy?

5. If you are used to Windows command line, there are some differences

the slash is the other way:
/ instead of \ (it's closer to your fingers while typing)
cd works
dir = ls (remember ls as list)
copy = cp
rename = mv (mv is actually moving, but you can move a file to another name)

6. Get used to tab completion

On the command line use the tab, tab is auto completion if you type the first few letters of a command and then tab it will try to fill in the rest. This works equally well with filenames. Try playing with it.

7. man is for manual

If you need to know how to use a command, type man [commandname] on the command line.
Try man man to get the man(ual) of how you can use man.

8. Find yourself a package manager

Package managers are programs which install software, almost every software you use in windows is available in Linux for free, with a package manager you can list and search trough available sofware and install problem free. If you're not used to Linux and coming from Windows, package managers are your life saver.

9. There's no such thing as .exe

In Linux there's no such thing as .exe files. If something is executable it has it's executable bit set.
You can find executables with ls -F this will show an asterisk * on every executable file.
use man ls to find more listing options.

10. Execute programs in the current directory with ./programname

Starting a program which is in the current directory is done by prefixing it with a ./ so the shell will start looking in the current directory.