try to make blocks of the same type collide to remove them. The indicators are on the left side. The larger circle (green) shows the block that will come out of block cannon next when you press fire (SPACE) and the smaller circle (yellow) shows the type of the block that will become next
Left arrow (cursor) / Right arrow (cursor) keys - move cannon\nSPACE - fire\nP - pause\nQ - quit\nIndicator on the right show which block will come out next and which one comes afterward, when you press fire. Larger circle shows next block, smaller circle shows the one that comes afterward. Those indicators on the left side are like Tetris indicators showing current and next block, but this time the blocks that you will fire, not the blocks that are gonna fall, those blocks are a surprise.