This is a whole new take on PvP. Essentially in WvWvW combat three worlds are pitted against each other, each world will have their home map and then there will be a fourth map, called the central map. The central map will be the largest map and were the majority of the combat and action will be occurring. This battle between the three different worlds takes place in an area called "The Mist".
There are many different goals in WvWvW. This can include capturing fortresses, gather resources, cut off supply lines to the other worlds, capture mines to give your world rocks to use in your catapults. The overall goal is to gain points and these points are gained through accomplishing tasks, the more points your world gains the more likely you will get a bonus for your world at the end of the battle with the two other worlds.
If enough points are gained your world can get a bonus for the entire world, even if a player didn't participate they will get the bonus. This can included XP bonuses to even increased item drops. Along with these points they help get your world ranked, this rank will determine the other worlds you compete against to make sure it is always a relatively even fight.
At any time during the WvWvW battle you can leave or join to help out. Since these battles can carry on for up to two weeks there are many opportunities to help your world out. There will be no restrictions on how many players from a world can join in the battle and help out. This means it is completely up to the players on the server/world to decide whether they want to win. There could be 100 people playing for one world and only 20 players for another.
This form of PvP is very laid back, which is meant to draw some of the more PvE focused players to play. It is unstructured in the sense that you can use as much strategy as you want or as little. You can go in by yourself and do what you can, or gather your friends and plan out strategies.
The side kicking system will also be implemented into WvWvW. So the lower level players will have a better fighting chance against the higher level players and doesn't restrict players to have to level up to a certain level first before they can compete.