Sure! The GitHub of the RCJ Soccer Sim has basic instructions to install everything. It also contains some simple code examples.
By the way, have you registered already? If not, please do so ASAP!
When you open the GitHub page (link below), click on the folder “Controllers” to access the code for each of the robots. You will see 7 folders (1 per robot + one for the artificial referee). You should not change the code in the referee folder.
The other 6 folders have code to control the 6 robots (3 from each team). You can use the code there as a starting point. To change the behavior of the robots, change the code from the file rcj_soccer_player_b*.py (blue team) or rcj_soccer_player_y*.py (yellow team). I hope that the comments in the code help you understand what you need to do.