In order to get into Pokemon at a casual, entry level, nothing is required. It is simply easy to just pick up and play for the story.
However, in order to reach the top level of play, you need to know how to manipulate Natures, EVs, IVs, know Egg groups and know Egg Moves. Nowadays, EVs and arguably Egg Groups are easy enough to learn; but the mechanics of passing down IVs and Egg Moves are still vauge and difficult to learn.
Thankfully, Sun/Moon made various things like EVs and IVs more clear and easy to manipulate. There is now a judge that lets you know what IVs your pokemon have and the pokemon's EVs can be seen on the status screen. Egg groups are and have always been based off the form of the pokemon (eg. human-shape corresponds to ones that are anthropomorphic in stature, field corresponds to pokes like Eevee and Rattata, etc.). Back before Gen VI, it was almost impossible to find out how EVs and IVs work on your own and you needed to manipulate the RNG to get the pokemon with proper IVs and Nature.
Edited by Orithan, 03 April 2017 - 06:34 PM.