Alola is far off region with no known neighbors. It consists of four main islands: Melemele Island, Akala Island, Ula'ula Island, and Poni Island with the artificial island of the Aether Paradise in the center. Each island has its own unique quirks and the terrain varies from island to island. Some of these environments include mountains, grasslands, lagoons, waterfalls, craggy cliffs, an active volcano, a desert, and a rainforest, among others. The general climate of Alola is warmer and more tropical than most other regions.
Alola is known for its culture, which sets it apart from many other regions that share a general structure, especially when it comes to their pokemon leagues. Instead of the typical league Alola has what is known as the island challenge for trainers to participate in. Instead of using what in other regions are known as HMs, Alola has a system of ride pokemon that are called in to assist trainers with traversing difficult terrain or removing obstacles.
Rather than a professor offering first partner pokemon to trainers each island kahuna does this job instead. A common selection includes Rowlet, Litten, and Popplio, though others such as Alolan Meowth are offered. The professors of the region include Professor Kukui, Professor Burnet, and Samson Oak. The island kahuna include Hala, Olivia, Nanu, and Hapu.
Each island is said to be guarded by a legendary pokemon known as the guardian deities. These include Tapu Koko on Melemele Island, Tapu Lele on Akala Island, Tapu Bulu on Ula'ula Island, and Tapu Fini on Poni Island.
The main villainous teams here include Team Skull, the Aether Foundation, and Team Rainbow Rocket, an offshoot of Team Rocket. Whether these groups are still active is up to you.
Alola is a great choice for characters that either live entirely on one specific island or that love to travel by boat to the other islands. It is a region with its own unique cultural traditions that set it apart from the typical formula for pokemon regions. There's a great deal more I could write about Alola's individual islands, but these overviews are meant to keep things brief. I recommend reading the Bulbapedia pages for more info on this one, even more so than some of my other guides.
