You know three cantrips of your choice from the onmyoji spell list. You learn additional onmyoi cantrips of your choice at higher levels, as shown in the Cantrips Known column of the Onmyoji table.

Preparing and casting Spells

The Onmyoji table shows how many spell slots you have to cast your spells of 1st level and higher. To cast one of these spells, you must expend a slot of the spell's level or higher. You regain all expended spell slots when you finish a long rest.

You prepare the list of onmyoji spells that are available for you to cast, choosing from the onmyoji spell list. When you do so, choose a number of spells equal to your Charisma modifier + your onmyoji level (min. 1 spell). These must be of a level for which you have spell slots. You may change your list of prepared spells whenever you finish a long rest

For example, if you're a 3rd-level onmyoji, you have four 1st-level and two 2nd-level spell slots. With an Charisma of 16, your list of prepared spells can include six spells of 1st or 2nd level, in any combination. If you prepare the 1st-level spell magic missile, you can cast it using a 1st-level or a 2nd-level slot. Casting the spell doesn't remove it from your list of prepared spells.

You can change your list of prepared spells when you finish a long rest.