There are a total of 7 regions in pokemon, with the 8th region coming soon. Here is the lists of all regions, including the Gen's that are in that region.
Image from https://flic.kr/p/32bq8A, made by Jirachi127
In order from Kanto-Alola, Ash Ketchum traveled through all of them, and each of them has a very special tournaments held in them, and pre-special battles as well, that you have to complete to earn a badge. When you have 8 badges, then you can enter the tournament.(Spoiler Alert) Ash has lost in all pokemon leagues except finally in Alola, he won.
