When you have a deep bite at the front and the upper incisors are tilted backwards, hiding a large part of the visible crown of the lower incisors, we may prefer to fit braces only on the upper jaw to begin with. The expected effect is that the upper front teeth move out of the way, and then we fit the lower braces. This movement can take a varying amount of time – from 1 month to 5–6 months.
In some patients, the lower teeth aren't expected to move as much as the upper ones, so we put off fitting the lower braces to give the patient a little more comfort for longer – wearing braces only on the upper jaw is easier to get used to, to clean and to eat with. We delay fitting the lower braces so that they need to be worn for a shorter time.
This answer is for general information. Your own case needs an examination by an orthodontist.