A signal booster connects between your aerial and your digital box. It strengthens or amplifies the signal you receive. It will not help if you are not in coverage. Similarly, it won’t help much if you are receiving poor reception because of things around your home such as trees or tall buildings.
It might help though if you are missing some channels due to a slightly weak signal. It is also useful if your rooftop aerial is connected to several TVs, since splitting the aerial (RF) cable to serve several appliances can weaken the signal received by your box.
However, we strongly recommend that you seek advice from a TV engineer, aerial installer or electrical retailer before buying a signal booster.