If you select 'button', a button input signal will be detected. The button channels are not a typical input for rc models because you really do not have them in your receiver. There you only get proportional channels. Some USB adapters convert a proportional input channel into a button signal (on / off). This is not a good practice, but it does exist. While using an RX2SIM, you will not see any button input channels in the input monitor. If you have a real button on your transmitter that is shown as a button in the input monitor, assign it here to the landing gear function. Then press the button on your transmitter and the landing gear changes state. If you release the button, the landing gear does nothing. When you press the button again, the landing gear changes state.

If you select 'Switch', a proportional channel or button will be searched for. If you assign the landing gear button here and press the button on your transmitter, the landing gear will change state. When you release the button, the landing gear changes state again.

If you select 'Slider or Stick', a proportional channel is searched for. Works as known in reality.