Almost all telescopic materials handlers have three modes for steering. From a training point of view it's probably easiest to start off in two wheel steer mode. In this configuration only the front wheels steer and it's the usual mode for traveling long distances and on public highways etc.
It should be explained that the steering mode should only be changed when the machine is stationary else serious damage to the transmission can occur. In addition, both front and rear wheels should be dead straight before the mode is changed. This is usually achieved by an indicator which lights up either front, rear or both to show that the steering wheels are pointing straight ahead.
The indicator shown here is from a Matbro machine but almost all use a similar system. As can be seen there are two green lights, one for front wheels and one for rear. The switch extinguishes the lights as they are not needed except when changing steering mode.
Steering should include driving both forwards and reverse and turning left and right. Quite a bit of space will be required for these manoeuvres and the instructor should make absolutely sure there are no pedestrians around at the time which is quite difficult to do on a building site!
Observation is critical on these machines and most serious accidents are caused by the operator not seeing hazards. Visibility to the right of the driver's cab is seriously impaired by the boom and usually mirrors are fitted to help the operator. These are to assist visibility and do not replace physically looking around.