OK - your tail rotor is there to generate a torque to counteract the turning effect of the engine pushing the main rotor around.
To do this, the tail rotor shoves a load of air sideways, thereby generating a horizontal force. Because the tail rotor is a long way from the main rotor mast - stuck out at the end of the tailboom - this makes a torque (force * distance from the axis of rotation) that stops the body of the helicopter spinning around.
BUT - there is now a net sideways force on the helicopter, so it will start to drift to the right (for anticlockwise turning rotors). Often this is counteracted by rigging the main rotor mast a degree or two off vertical.
Of course it doesn't stop there... Because the tail rotor is lower than the main rotor you now have a couple that will roll the body to the left, so the machine tends to hover left skid low, which is one reason why the pilot has to sit on the right.... and so on it goes.