Brief how to work VFD?

vfd operate and protect and control motors by controlling the frequency of the AC input 

there are different ways to work with vfd for motor speed controlling.

1)Source of frequency command which may be through digital keypad,Potentiometer,0 - +10V input on AVI terminal or 4-20mA input on ACI terminal,Rs485Comm.port

2)Source of Operation command which may be through digital keypad,external keypad stop(effective/ineffective),Rs485 comm port keypad stop (effective/ineffective)

Motor frequency can vary according to our requirement

what do you mean? I didn't understand you