Developers
Developers are the people/group which create the game. These people are involved in most aspects of the creation of the game from the story to the technical aspects of the game creation. The game development would most likely be split upon various teams which do single jobs which then get compiled at the end to create a full game.
Publisher
The publishers are the people/group that finance the Game Developers and maybe help the developers out. the Publishers also distribute the games that are created. the publishers can also hire extra staff for certain areas if needed.
Console Manufacturers/First Party Companies
Console Manufacturers/First party Companies are the companies that create the game consoles and the people that create the games that are exclusive to their console. examples are Sony's Playstation with Crash Bandicoot, Microsoft's XBox with Halo.
Distribution and Retail
This sector of the Game Industry deals with the distribution of the games that developers create, this sector gives the games to various retailers and then the retailers sell the games to the public, examples of game retailers are Games, Steam etc.
Outsourcing Companies
This sector of the gaming industry allows for parts of development to be completed outside the company. this is used when there is nobody capable of doing a certain task to a high level. this can also speed up the process of the while operation by giving an outside company work to do whilst the main developers handle other tasks.
Press and Media
The Press and Media receive the game last and they are the sector that handles the advertisement of the game, they also write things about the game i increase the sales/rating of the game. The press and media also handle the announcement of the game.