To brush with tooth powder, simply dip your toothbrush into the powder, or carefully squirt some onto a wet toothbrush. Brush teeth as usual.
Follow with homemade mouthwash if desired.
Bentonite clay loses its beneficial properties when it comes into contact with metal, so it's best to use plastic or glass when mixing and storing your tooth powder.
Particles of the tooth powder are fine enough that a small squirt bottle like this can also be used (as long as you don't get the squirt-tip wet, which will cause clogging).
If using the dip method to get the homemade tooth powder onto your toothbrush, you may want to consider giving each family member his/her own container.