Killing the ender dragon once will give you a Dragon Heart; this will be used to craft Awakened Draconium; you will need a healthy supply of these hearts in order to progress into the mod.
There is so much misconception with Draconic Evolution and summoning the ender dragon that people (including myself) search frantically, trying to find out how to summon the ender dragon again after you have killed it.
There is no secret within the mod, and it’s not hidden; Minecraft has its very own way of summoning the ender dragon again with END CRYSTALS. Placing 4 of these around the portal, in the end, will start the summoning process.
In previous versions of the mod, you would need to put down certain blocks in a certain pattern and summon the dragon. This is no longer the case.