The phrase "to brush one's hair" means to use a comb or brush to run through and style one's hair. This action is usually performed in the morning as part of personal grooming routine, but can also be done throughout the day to keep hair neat and tidy. Brushing helps distribute natural oils from the scalp evenly along the length of the hair, and can also help remove any tangles or knots that may have formed during sleep. Additionally, brushing can stimulate blood flow to the scalp and promote healthy hair growth.