Do you know how to get an element from a "1D" ArrayList? If so, you basically do the same thing twice witha "2d" ArrayList. It sounds like you might need some more help with the Collections Framework in general. You should take a look at the Collections Trail from Sun's Java Tutorial. You should also take the time to become intimately familiar with the API documentation for the version of Java you are using.
After reviewing the links I have given above, please come back with more questions if anything is still unclear.