The jellyfish starts out as larva. It swims around till it finds a solid surface then fixes itself to the surface and overtime, it transforms into a polyp.
The polyp then starts the process of strobilation, this is where it begins to develop horizontal lines across the end of its body. The lines eventually deepen enough for the discs to separate and the one at the top develops the quickest into a baby jellyfish, also know as the Ephrya.
The Ephyra discs wait until they are 96% liquid, this is when they become an adult.
Now that the jellyfish is finally an adult, they are able to produce eggs and sperm, repeating the process.