Although there are no instructions in game (by purpose), the first level forces you to figure out the basics.
However, the second level introduces the defensive pillars, and that might be difficult to figure out that there are two different places on them to put those embers/jewels, whatever they are.
One place increases the power, second place shoots with the current power level.
Didnt have time to make something that would have hinted about them, was thinking of adding sparkling effect or something on them to indicate player that you can do something with them.
I did mention it in the games page, but theres lot of stuff there, so not sure people will notice it.