Player Core
Chapter 7: Spells
Ranges, Areas, and Targets
Source Player Core pg. 298
Spells with a range can affect targets, create areas, or make things appear only within that range. Most spell ranges are measured in feet, though some can stretch over miles, reach anywhere on the planet, or go even farther!
Touch Range
Source Player Core pg. 298
A spell with a touch range requires you to physically touch the target. You use your unarmed reach to determine whether you can touch the creature. You can usually touch them automatically, though the spell might specify that they can attempt a saving throw or that you must attempt a spell attack roll. If an ability increases the range of a touch spell, start at 0 feet and increase from there.
Areas
Source Player Core pg. 298
Sometimes a spell has an area, which can be a burst, cone, emanation, or line. If the spell originates from your position, the spell has only an area; if you can cause the spell's area to appear farther away from you, the spell has both a range and an area.
Targets
Source Player Core pg. 298
Some spells allow you to target a creature, an object, or something more specific. The target must be within the spell's range, and you must be able to see it (or otherwise perceive it with a precise sense) to target it. At the GM's discretion, you can attempt to target a creature you can't see, as described in Detecting Creatures. If you fail to target a particular creature, this doesn't change how the spell affects any other targets the spell has.
If you choose a target that isn't valid, such as if you thought a driftdead was a living creature and targeted it with a spell that can target only living creatures, your spell fails to target that creature. If a creature starts out as a valid target but ceases to be one during a spell's duration, the spell typically ends, but the GM might decide otherwise in certain situations. Some spells restrict you to willing targets. A player can declare their character a willing or unwilling target at any time, regardless of turn order or their character's condition (such as when a character is paralyzed, unconscious, or even dead).
Spells that affect multiple creatures in an area can have both an Area entry and a Targets entry. A spell that has an area but no targets listed usually affects all creatures in the area indiscriminately.
If you choose a target that isn't valid, such as if you thought a driftdead was a living creature and targeted it with a spell that can target only living creatures, your spell fails to target that creature. If a creature starts out as a valid target but ceases to be one during a spell's duration, the spell typically ends, but the GM might decide otherwise in certain situations. Some spells restrict you to willing targets. A player can declare their character a willing or unwilling target at any time, regardless of turn order or their character's condition (such as when a character is paralyzed, unconscious, or even dead).
Spells that affect multiple creatures in an area can have both an Area entry and a Targets entry. A spell that has an area but no targets listed usually affects all creatures in the area indiscriminately.
Line of Effect
Source Player Core pg. 300
You usually need an unobstructed path to the target of a spell, the origin point of an area, or the place where you create something with a spell. You can find more information on line of effect here.