E-bike ABS monitors the speed of both wheels. If the front wheel is about to lock, it reduces pressure in the front hydraulic brake, helping preserve steering on surfaces such as gravel.
The Bosch system also limits rear-wheel lift during hard braking. Electronics work with specifically matched brake components; simply replacing a brake lever is not enough.
Bosch e-bike ABS is available on factory-equipped bicycles, rather than as a retrofit kit. That makes it a feature to consider before buying a bicycle.
Practise braking in a safe, controlled space. Having electronic assistance is a good reason to learn how your bicycle responds before taking it into traffic.