The raised central tuft is a row or bundle of bristles positioned slightly higher than the rest of the brush surface. Because the overall bristle arrangement is arched, this tuft sits close to the natural contours of the teeth and can make better contact with the depressions and uneven areas on the chewing surfaces. In the product description, it is described as helping lift plaque from these uneven areas and giving a mild polishing effect to the enamel. That generally means it reaches areas where a completely flat brush surface might simply pass over.
For practical purposes, this tuft matters most when you brush the chewing surfaces of the molars and premolars, where the grooves tend to collect food and plaque. It is not a replacement for flossing or professional cleaning, and it does not whiten or restore enamel. It simply adds a little more contact where the tooth surface is not smooth.
To use it effectively, move the brush back and forth in short strokes over the chewing surfaces, letting the tuft follow the natural pits and fissures. There is no need to press down hard; the height difference between the tuft and the surrounding bristles is enough to reach into those spaces.