Signals are normally given by direction indicators and/or brake lights. There are occasions when an arm signal can be helpful. It's important that you use the correct signal.
Purpose Use signals
to let others know what you intend to do to help all other road users, including pedestrians in good time and for long enough to allow other road users to see the signal and act upon it.
When to signal
Signal in good time, particularly before turning right or left overtaking another moving vehicle moving from one lane to another. Signalling too soon can confuse rather than help - for example, when there are several side roads very close together. Signalling too late can cause following vehicles to brake hard or swerve. Watch out for situations which call for special timing in signalling. For example, when you signal to pull up on the left, make sure there isn't a junction just before the place you intend to stop. If you signal left too soon, a driver waiting at that junction might think you intend to turn left. Delay signalling until you're in a position where your signal can't be misunderstood.
A signal might not be necessary where there is no-one to benefit from it, or where the signal could confuse other road users. Consider whether a signal is necessary before moving off pulling up passing stationary vehicles, when you can position early and maintain a steady course.
signal carelessly wave pedestrians across the road fail to check that the signal is cancelled after your movement is completed mislead other road users. Always use the correct signal.
Nowadays, arm signals are seldom used. However, there are occasions when you might need to use one. Approaching zebra crossings When yours is the leading vehicle, using an arm signal when slowing down or stopping can be helpful.
This not only tells following traffic that you intend to stop, but also approaching traffic and waiting pedestrians, who can't see your brake lights. Turning right Use an arm signal when necessary to emphasize a difficult right turn on a road carrying fast-moving traffic to turn right just after moving out to pass a stationary vehicle. Stopping Use the 'slowing down' arm signal where any confusion to other road users might be caused by a 'left turn' indicator signal.
Brake in good time. If necessary, lightly press the brake pedal early, or more than once, to show your brake lights to following traffic.