Toilet training is a learning process, not a disciplinary process, and a complicated one at that! Your child has to understand what you want, and then has to learn how to do it. In addition to understanding the bodily sensations, getting to the bathroom and getting clothes off, a child must first constrict sphincter muscles to achieve control, and then relax them to eliminate. Obviously there is a lot to learn. Gaining bowel and bladder control is a skill and fortunately children usually like to learn new skills.
The mastery of skills usually follows a pattern. First comes bowel regularity often followed by bowel control. Daytime bladder control often comes next but for many children this can happen simultaneously, and finally later (often much later), comes nighttime bladder control.
Not every child will follow this pattern, of course. While girls often achieve control before boys, brothers have been known to be dry before same-age sisters. Also, it is not uncommon, especially for boys over the age of 3, to have bladder control but not have bowel control. And, of course, there are children who achieve daytime and nighttime control simultaneously. With the swing toward a more relaxed approach to toilet training from the previous generation, children tend to be trained later and more frequently their bowel and bladder functions come under their control at the same time.