Health is a Value that determines the continued function of your body and your consciousness. Should you health fall to zero, you fall unconscious and risk death.
Health is determined by a dice roll at each new level, affected by your class and vitality attributes.
The level of class attained when gaining XP directly dictates the amount of D6 dice one rolls, based on the type of class, to to determine health, the result is then affected by a modifier from that class, and then added to by the vitality attribute to come to your final value. Instead of rolling, a player may choose to instead to take the dice's "average", which is found by summing the total of the dice you would have rolled, halfing the value and adding one health per each dice in the tally.
For example, if your class requested that you roll 2D6+3 for your health value but you wished to take the 'average' the calculation would be as follows:
((2d x 6) ÷ 2)(1x2d) + 3 or half dice max value plus one for each dice, plus three class modifier.
Which is 8 dice "average" + 3 or 11.
And if you Vitality was +3, then it would be 8 + 3 + 3 or 14.
Lightweight Classes utilise a D6, and their modifier ranges from a +1 to a +3.
Brawler Classes utilise 2D6, and their modifier ranges from a +1 to a +3.
Titan Classes utilise a 3D6, and their modifier ranges from a +1 to a +3.
Therefore in one level, a Lightweight could get as little as 2 health, and as much as 9, a Titan could get as little as 4 health, and as much as 21.