How do combos work in Guild Wars 2?

Solution 1:

Each combo begins with a Combo Field that places an AoE/barrier field and ends with a Combo Finisher, which is triggered by Blasts, Leaps, Projectiles, or Whirl finishers. You can see in the description of a skill whether or not it will combo. If a skill can combo at all, it will list it as the last item in the skill description.

The following table shows the different types of interactions.

Field        Blast Finisher     Leap Finisher   Projectile Finisher     Whirl Finisher

Dark         Area Blindness     Blindness       Life stealing           Leeching Bolts
Ethereal     Area Chaos Armor   Chaos Armor     Confusion               Confusing Bolts
Fire         Area Might (x3)    Fire Armor      Burning                 Burning Bolts
Ice          Area Frost Armor   Frost Armor     Chilled                 Chilling Bolts
Light        Area Retaliation   Retaliation     Remove Condition        Cleansing Bolts
Lightning    Area Swiftness     Dazing Strike   Vulnerability           Brutal Bolts
Poison       Area Weakness      Weakness        Poison                  Poison Bolts
Smoke        Area Stealth       Stealth         Blindness               Blinding Bolts
Water        Area Healing       Healing         Regeneration            Healing Bolts 

Combo fields actually can be done by a single character, as long as you start with a skill that is labeled Combo Field and end with a skill that is labeled Combo Finisher.

For example, when a Ranger uses the Torch's offhand Bonfire skill, they can then use Splitblade Axe main hand skill to throw the axes through the Bonfire and create burning projectiles axes that cause Bleeding!

Solution 2:

In Guild Wars 2, certain skills will lay down one of nine types of Combo Fields. Any skill with a Combo Finisher tag, when used in/through this field, will have a special effect. A full table of interactions between Combo Fields and Combo Finishers can be found on the wiki, here. Combo Finishers are not restricted to your own Combo Fields, but can also interact with others' Combo Fields. A Finisher can only interact with a single Field at a time. It is currently unknown how the game determines which field to use in the case of multiple overlapping fields.

Solution 3:

Inorder to create a Combo you will need two things

A Combo Field, which is any AoE skill labeled "Combo Field" in its description, and a combo finisher, which is any skill named Combo finisher.

There are Four Types of Combo Finishers; Projectile, Leap, Whirl and Blast, each creating different effects when entering a combo field.

The Stats of the player using the Combo Finisher goes on the stack and not the one using the Combo Field