Working at the command line

Command-line vs. Dev tools If you've come from programming classes where you've grown accustomed to using dev tools like Eclipse, you will first need to get comfortable with programming at the command line. What this means:

On Mac-OS: You will need to learn how to edit, compile and execute using the terminal. You will need to use the ls, mkdir, cd and cd .. commands at the terminal. It helps to know other commands like mv and rm, but you can manage to do the same with Finder.
On Linux: Well, you already know how to work at the commandline. (It's more or less the same as on the Mac.)
On Windows: You will need to learn how to edit, compile and execute using the command-prompt. You will need to use the dir, mkdir, cd and cd .. commands at the command prompt. It helps to know other commands like ren and del, but you can manage to do the same Windows-Explorer.

All told, you'll need to spend a couple of hours to get this working, and will get more practice as you proceed in the course.

Editing programs:

On Mac-OS: Mac-OS comes with the pico and vim editors for the command-line. Generally, pico is easier to learn. If you're up for it, Emacs is a more sophisticated editor, preferred by Unix hackers, but difficult to learn initially.
On Windows: Not all versions of Windows come with a default command-line editor. You can install the nano editor (which is a version of pico) yourself - it takes a little doing, but it's worth it because you will have a solid editor. Otherwise, you will need to use Notepad. You can also install Emacs and go through the stiff learning curve.

Use the Terminal (Mac/Linux)

Practice using the commandline. Try to achieve the following in sequence:

View a couple of videos on youtube that show you how to use the Terminal on Mac-OS. This is just to get a general idea.
Create a directory (folder) for the course called testdir off of your Desktop using Finder.
Open a Terminal by searching for the app using Spotlight (the spyglass at the top right).
Type pwd at the command line to know which folder (directory) you are in. Then type ls to see which files are in the folder. You should confirm by looking at the same folder in Finder.
Type cd Desktop at the command line, then cd testdir to put you in the linAlg folder.
Type pico HelloWorld.java, which puts you into the pico editor, where you can see the editing commands at the bottom of the window. Type in the standard HelloWord.java program, then save and come out back to the terminal commandline. For reference, here's the standard HelloWorld.java program.
Compile HelloWorld.java by typing javac HelloWorld.java at the command-line. It should compile. If not, fix the errors and repeat.
Execute the file by typing java HelloWorld at the commandline. It should print "HelloWorld!" as desired.
Now use mkdir to create a new sub-folder called testdir under linAlg and write another Java program to test. Then type cd testdir to enter the directory.
Go back up to the linAlg folder using cd .. and type ls to see that you're in the right folder.

Use the Command-Prompt (Windows)

View a couple of videos on youtube that show you how to use the command-prompt. This is just to get a general idea.
Create a test directory (folder) called testdir off of your Desktop using Windows-Explorer.
Open a Command-Prompt window. Doing this is different on various versions of Windows, so look it up on youtube or elsewhere. It typically opens a dark looking window with very little text.
Type cd at the command line to know which folder (directory) you are in. Then type dir to see which files are in the folder. You should confirm by looking at the same folder in Explorer.
Type cd Desktop at the command line, then cd testdir to put you in the testdir folder.
You now need to use an editor. I will assume you've installed the nano editor, which you can get from here.
Type nano HelloWorld.java at the command prompt, which puts you into the nano editor, where you can see the editing commands at the bottom of the window. Type in the standard HelloWord.java program, then save and come out back to the terminal commandline. For reference, here's the standard HelloWorld.java program.
Compile HelloWorld.java by typing javac HelloWorld.java at the command-line. It should compile. If not, fix the errors and repeat.
Execute the file by typing java HelloWorld at the commandline. It should print "HelloWorld!" as desired.