Robocode is a game whereby you write Java code to control the behavior of a tank on a virtual battlefield. The tanks are randomly placed and then they're on their own to do whatever you've commanded them to do. I've found a good Robocode tutorial for people wanting to get started. Specifically, you may wish to check out the "Guide to Robocode" section and then progress to the "My Second Robot" tutorial. The rest of the tutorials go on from there.

Just a few notes on using jar files... Running Java programs packaged as jar files (like the Robocode installer or the unpacked Codesize tool) is easy. Just use the "java -jar filename.jar" command. To unpack a jar archive (like the Codesize package), use the "jar xf filename.jar" command.

The offical Robocode page provides links where you may download the Robocode installation jar program. For obvious reasons, you should already have Java installed on the host where you will be running Robocode. The Robocode package provides you everything you need to get started writing Robocode robots. It has a Java editor and will use your installed JDK for compilation if you have it, or download an alternative if you don't. It contains options for packaging your robot up into a jar file. Most importantly, it has Sun-Java-style documentation in the javadoc subdirectory of the installation directory (just open the index.html file in a web browser).

The page also provides a number of useful links for participants of all skill levels, not the least of which is the Robocode Wiki. Don't be daunted by the Wiki: there's a lot of information, just be persistent. When first getting started, the sample robots are great examples; don't forget to give them a look (they're in the robots/sample subdirectory of your Robocode installation directory).

When participating in different Robocode events, sometimes alternative "bot categories" will be used. I would suggest that you download the Java Codesize tool and unpack it into your Robocode installation directory if you intend to participate in such events. It basically amounts to a limitation on the number of bytes of Java bytecode that you're allowed to utilize in your robot. It can be very challenging.

Since I'm not a fan of the integrated editor (and prefer Emacs anyway), I have provided a sample ant file for Robocode robots. Just modify the properties in the "init" target as appropriate. Most importantly, be sure the path to your Robocode installation directory is correct. That path is used to reach the directory where your robot should be installed as well as to reach the Codesize tool. Place the build.xml file into the directory with your robot's .java file and run the "ant" command. It supports targets to compile (just build the class file(s)), buildjar (to construct a jar file), see codesize (gives a codesize readout of your robot), install (install your robot to the robots subdirectory of the Robocode installation directory), and clean (clean up the mess).

I don't claim to be any kind of expert on writing Robocode robots. This is only intended as a quick-start guide to reduce the barrier to entry into getting started with Robocode. Good luck!