Above all else, the main thing you need to know to use Robowar is its unique programming language: Robotalk. Robotalk is an unusual programming language based upon that of the HP calculators. It is based on a stack of numbers and instructions. Numbers on the stack can be added, subtracted, multiplied, divided, stored, recalled, put on, removed, moved, swapped, rolled, and generally manipulated(you get the picture). Other functions can also be done.
There are two kinds of instructions Operators and Registers, and as their name suggests, operators do something, either to the robot or to the stack. Registers don't do anything, bu are typically acted on by an operator. This can mean altered or used to alter some parameter of the robot.
In addition, there are interrupts, an advanced programming feature which greatly enhances the efficiency of robots. These work by having the program branch to a certain part of the code after a certain register goes over a certain threshold. They save much processing time and are really essential for your robots to use if they are to have any hope of competing with today's powerful robots.
Robowar comes with a nice online documentation covering all facets of Robotalk, along with the interface and some history, so, if you are working on your code and want to know how to do something properly, consult it.
Now that you know your way around Robowar, on to the good stuff.