What is a Ritual
Ritual is a classifications of spell that requires special effort to cast with often a longer time. When you cast a ritual spell, it does not use a spell slot unless stated other wise.
Primary Caster
When you take charge of a ritual, you are its primary caster,
and others assisting you are secondary casters. You must know the ritual spell, and must be a spellcaster to cast a ritual spell. You must succeed a spellcasting check based on the DC as seen below. If the ritual spell is equal or lower to your heightened level, you do not need to make a check and it auto succeeds
Secondary Caster
Many rituals need additional secondary casters, who also don’t need to be able to cast spells. Unlike a primary caster, a secondary caster doesn’t need a minimum level or skill proficiency. The Secondary Casters entry, if present, indicates the minimum number of secondary casters required. The secondary caster may also use any skill the GM allows instead of a spell casting check
DC
The DC of a ritual spell is equal to 12 + 3 x the spell level
Secondary Check
A secondary check is rolled with a result of
Critical Success You gain a +4 circumstance bonus to the primary check.
Success You gain a +2 circumstance bonus to the primary check.
Failure You take a –4 circumstance penalty to the primary check.
Critical Failure As failure, and you reduce the degree of success of the primary skill check by one step.