Your saving throw scores appear on your 'score' sheet.
Reflex - Based on dex, classes like rogues tend to have high reflex saves. A
high dexterity increases your reflex save, an extremely low dexterity can
lower it. Offensive physical spells are generally those which would require
one to make a reflex save, in an attempt to dodge or somehow get away from
the effect. Two examples of spells with a reflex save would be fireball and
chain lightning.
Fortitude - Based on con, classes like warriors tend to have high fortitude
saves. A high constitution increases your fortitude save, an extremely low
constitution can lower it. Spells which will attempt to affect your stats or
resistances, or cause a system shock by causing a massive amount of damage of
some sort are those which would require a fortitude save. Two examples of
fortitude spells would be weaken, which reduces one's strength, and
disintegrate, which tries to disintegrate your body.
Will - Based on wis, classes like mages and priests tend to have high will
saves. A high wisdom increases your will save, an extremely low wisdom can
lower it. Spells which attempt to affect your mind, dominate you, charm you,
force you to do things against your will, or turn your own mind against you
are will saves. Two examples of spells with will saves would be sleep and
cause light wounds.