To get into any VG World Tournament, you have to secure an invitation. For Pokemon at least, this invitation is secured when you have sufficient championship points. People who receive these are usually the top players from they're respective regions.
Championship points can be earned by participating and winning a place on the podium in competitions. Eg.- Participating in the South California regionals and winning 1st place gets you Championship points.
Here's how the points are distributed among the participants:
Online Competitions:
![enter image description here][1]
NOTE: To receive Championship Points or Play! Points for an Online Competition, players must have a Player ID before the competition begins. In 2015, points will not be separated by region but will be awarded to the top 256 players worldwide, per age division.
Premier Challenges:
![enter link description here][2]
Regional Championships:
![enter link description here][3]
National Championships:
![enter image description here][4]
So, now suppose you have collected points. Your number of points will be counted and you will be ranked in your region. If you happen to rank high enough, you get an invite to Worlds. Every region has a different rank limit, some allow you if you are in the Top 40s and some don't even allow you if you aren't in the Top 2. Rank limits are also different for every division.
Here's how it goes:
![enter image description here][5]
Hope I helped!
[Source 1][6] (For how to secure the invite)
[Source 2][7] (For information on Championship points)
[1]: http://i.imgur.com/FErYMCT.png
[2]: http://i.imgur.com/elkPeUE.png
[3]: http://i.imgur.com/qLDP9V5.png
[4]: http://i.imgur.com/vD0Cvl9.png
[5]: http://i.imgur.com/PiHgFY8.png
[6]: http://www.pokemon.com/us/play-pokemon/pokemon-events/pokemon-tournaments/vg-world-championships/
[7]: http://www.pokemon.com/us/play-pokemon/pokemon-events/pokemon-tournaments/vg-world-championships/
