Saving throws against creatures

[Sparkly Panda]

My friends and I started a new campaign with a relatively new pathfinder DM. One of my friends is a witch and was wondering how the saving throw against creatures worked. For example, he would cast a spell, and the target has a saving throw to half the damage if he/she/it succeeds. But how do you know what's the saving throw number?

-Sparkly Panda

[Are]

Each creature in the Bestiary has a line listing the numbers to add for each saving throw. For instance, a Dire Ape rolls d20+7 for Fortitude saves, d20+6 for Reflex saves, and d20+4 for Will saves, due to the "Fort +7, Ref +6, Will +4" line in its statblock.

The number the creature has to reach to successfully save against one of the witch's spells is "10 + the spell's level + the witch's INT modifier". So, for instance, if a witch with an INT of 18 casts a 1st-level spell, the number to beat is 10+1+4, for a total of 15.

Hexes work slightly little differently, as the number to beat is instead "10 + half the witch's level + the witch's INT modifier".

[DM_Blake]

You will find this in the description of the witch class (or any other class that can cast spells).

Specifically, the Witch says (under "Spells" in the Witch class abilities):

To learn or cast a spell, a witch must have an Intelligence score equal to at least 10 + the spell level. The Difficulty Class for a saving throw against a witch’s spell is 10 + the spell level + the witch’s Intelligence modifier.

Every spellcasting class has this information, but it's not always Intelligence so check each class as needed.