the basic rules are as follows:
1. line up the same shapes into the same road by pressing the cross-pad as the shapes move into the center crossing area.
2. when you get 5 of the same shape you begin stockpiling that one type - the more of the same shape you can direct into that road the bigger and bigger your stockpile gets (shown by the big geometric shape by the side of the road)
3. send a different shape and you lose that road's stockpile, *unless* you have a stockpile on another road, then the stock flies and merges regardless of the shape - and this is where it gets fun - if you have two remaining stockpiles, the stockpile *doubles* because it merges with both the remaining roads, this is what you need to aim for.
4. On the right there is a guage with a "danger bar" closing in on your "puck" - in order to fire shots at your puck you need to "fire" your stockpile. This is done by using the "attack piece" which are the siren-sounding cars. You push A to use one of these and you collect them as you play.
5. if you manage to get all 4 roads stockpiling you enter into "Autobahn" (the background changes to a spiral effect), this is a sudden death mode where the speed of the cars increases and increases and you really test your reflexes. If you make one mistake you are dumped out of this mode, but you get a free "attack car" and the stock you just messed up on gets fired at the puck.
6. When a stockpile on a particular road reaches the MAXed out circle shape it will automatically fire at the puck - however, you can cause a chain reaction by repeatedly causing it to merge with another road before it is fired. By getting the hang of this you can combo-up to some ridiculously high shot counts.