Basics
Players have two types of Ki points: Internal Ki and External Ki. Each pool of Ki is equivalent to half their total player level rounded down. For example, a level nine player has four Internal Ki points and four External Ki points, as 4.5 rounded down is four.
Some features can only use one type of Ki. If a feature is unlabeled, assume that it can use either. Using a Ki feature requires a bonus action, unless a feature states otherwise.
For any Ki Techniques that require rolling against a save DC, your save DC is your highest base stat modifier + your proficiency bonus + 8.
They reset every long rest, or if a person takes time to meditate (1 hr at the minimum), they gain back one Ki point for every hour meditating.
Using Ki And Spirits
In making any rolls that involve trying to make an action that involves communicating with Spirits (Race) that cannot communicate through normal means (i.e. being unable to speak mortal languages), or interacting with the spiritual energy in the environment, the roll is 1d20 + you proficiency bonus modifier. The user can expand Ki points from either pool to add to their Spirit roll.
EX: The party is trying to discern what a stubborn Spirit blocking the road wants. The Spirit cannot communicate in any mortal languages. To help read this enigmatic entity, a level 6 PC, which has a proficiency bonus of +3, expends two Ki points to add +2 to their roll. They would roll a 1d20+5 to read this Spirit's character.