There are times when misfortune or unpredictable peril befalls a hero. Only luck or their own natural hardiness can save them from disaster, and to do so they must make a saving throw.
Saving throws come in three kinds. Physical saves relate to challenges of physical endurance such as poisons, diseases, radiation, or dire exhaustion. Evasion saves involve dodging explosions, evading falling hazards, diving back from a crumbling surface, or other-wise exerting one’s powers of speed and swift reaction.
Mental saves relate most often to psychic influences, hallucinations, esoteric mental control technologies, and other perils that assault a hero’s mind or perceptions. Mental saves can also be used when no other saving throw category seems to apply and only blind luck and ineffable intuition can save the hero.
Your character’s saving throw scores start at 15, and decrease by one point each time you advance a level. Each saving throw is modified by the best modifier of two different attributes: Physical by the better of Strength or Constitution, Evasion by the better of Dexterity or Intelligence, and Mental by the better of Charisma or Wisdom. Thus, a first-level PC with a Strength of 5 and a Constitution of 14 would have a Physical save of 14.
To make a save, roll 1d20 and try to equal or beat the appropriate saving throw score. On a success, you evade or mitigate the peril, while on a failure it takes full effect. A natural roll of 1 is always a failure, and a natural roll of 20 is always a success.
The GM decides when a saving throw is appropriate. Some dangers might not allow one at all.