Need some help about 3.1.2

when armed, motors do not spin. I have tried to set it up to ‘very slow’ or ‘slow’ it still cannot spin,but if I push throttle up,motors will spin and copter works as usual. I am confused. Some help would be great.

Make sure that your ESCs are calibrated.
Make sure that your radio is calibrated.
If all else fails, use the advanced parameter list to set MOT_SPIN_ARMED higher.