As the game proceeds, you and your opponent take turns placing fissile material on the game board cells. You can put material on any cell, so long as your opponent doesn't currently occupy it.
A cell reaches critical mass when it has enough material to contaminate all of its adjacent cells (horizontally and vertically adjacent only, no diagonals). When a cell goes critical each of the adjacent cells gains an additional piece of fissile material. If your opponent occupies the cell, you gain control of the cell and all of its fissile material.
What makes the game challenging is the potential for chain reactions. If a cell reaches critical mass and spreads to its adjacent cells, those cells have the potential to go critical. Since more than one cell could go critical at the same time, you can end up with simultaneous explosions spreading material throughout the game board.
Trying to consider the complete chain of events resulting from a single placement makes for complex strategies and endless fun.
Good luck!
For demonstration purposes, your Palm can play against itself at all skill levels. You can use this to get a feel for the game and as a way to understand strategies.
You have the ability to Undo a move under the (unlikely) circumstance where you make a bad move and would like to try something else.
Finally, your Palm can suggest a move for you to make. The intelligence level is based on the current skill level setting for the Palm so that it will give you advice at it's current level of expertise. Due to the simplicity of the Novice level, suggestions will be made at the Intermediate level if Novice is the current skill level.
Feel free to contact me at zapp@computer.org with any issues, comments, etc.