Refer to figure.
Roll, pitch and yaw are the three axes of rotation for a helicopter, they are the three axes that a helicopter can rotate around. The three axes are perpendicular to each other and passing through the Centre of Gravity (CG).

Roll: refers to rotation around the longitudinal (front-to-back) axis of the helicopter. This causes the helicopter to tilt left or right. This is controlled by the cyclic stick, which is held by the pilot in the cockpit. When the pilot tilts the stick left or right, the helicopter will roll in the corresponding direction.

Pitch: refers to rotation around the lateral (side-to-side) axis of the helicopter. This causes the helicopter's nose to tilt up or down. This is controlled by the collective lever, which is also held by the pilot in the cockpit. When the pilot pulls back on the lever, the helicopter's nose will tilt up, increasing the pitch angle. When the pilot pushes forward on the lever, the helicopter's nose will tilt down, decreasing the pitch angle.

Yaw: refers to rotation around the vertical (up-and-down) axis of the helicopter. This causes the helicopter's nose to rotate left or right. This is controlled by the pedals, which are located near the pilot's feet. When the pilot pushes on the left pedal, the helicopter's nose will rotate to the left, and when the pilot pushes on the right pedal, the helicopter's nose will rotate to the right.

It is important to note that to fly the helicopter the pilot must coordinate the movement of the cyclic stick, collective lever and the pedals. A good coordination of these three control devices will result in a smooth and safe flight.

Also, these three axes of rotation are used to perform different types of manoeuvres such as hovering, climbing, descending, forward flight and many more.