Bushes are used on cars as hinges on the suspension, they allow the car to move up and down during driving without the wheel alignment moving out of alignment. They are made of a type of rubber and have an extremely hard life. As a result over time they wear resulting in un-allowable movement in the suspension.
Typically this results is loss of feeling in the front end of the car with play in the steering wheel. In some cases there may be an associated thump noise from the suspension when driving. If they’re bad this also wears the tires. If they are bad it can make it hard to control the car, meaning you can crash.