In DJ there are essentially 3 levels to magick. The lowest is preternatural, with supernatural and deital coming in order after the first. The energy of supernatural magick is 10 times that of preternatural, and deital 10 times that of supernatural
In each level―preternatural, supernatural, and deital―there are ten grades, from I-X. Though in the case of Grade X preternatural and supernatural castings you could consider them respectively Grade 0 supernatural or deital castings.
If you like you could have a mundane level of magick. Magick that really can’t do all that much and which costs very little in the way of power. Maybe something like 18 points of heka to cast a Grade X mundane casting, which would be the equivalent of a Grade 0 preternatural Casting.