Of the Ability Stats, Fortitude represents raw physical strength, as well as resistance to physical attacks, disease and pain.
Fortitude increases Hit Points linearly.
|Points||Hit Point Increase||Hit Point Total Bonus|
Along with adding 1/2 Level to attack damage, you also add your Fortitude score to melee attacks. A higher Fortitude score means more damage when you hit.
Fortitude score is added to your Athletics skill check rolls.