Health represents how much damage a character can take before it dies. It can be seen as a red bar over the mana bar in the interface. Health regenerates over time, but sitting will make it recover faster.
health points = level * a + constitution * b - 170
where a and b have these values depending on class:
|Archers and mages:||37||18.5|
If the result ends in .5, it is rounded down. So for example, a level 33 marksman with constitution of 58 will have:
33 * 37 + 58 * 18.5 - 170 = 2124 health points
Or a level 47 barbarian with constitution at 85 will have:
47 * 47 + 85 * 23.5 - 170 = 4036 health points
Constitution also increases the regeneration rate of a character's health. Given their more favourable formula as well as generally higher constitution, warriors have the highest max health amounts, with archers having slightly more health than mages.