How much gate-source voltage should be applied to drive the MOSFET?

On-resistance stated in the datasheet: RDS(ON) Apply the gate-voltage value under the measurement conditions. Or use this value as a reference.

Fig. 1:VGS ― RDS(ON) property
Fig. 1:VGS ― RDS(ON) property

The on-resistance between drain and source is large when the channel is not formed sufficiently at the gate threshold voltage, and it is inappropriate to set the gate threshold voltage in the on-resistance measurement condition. The gate voltage for the measurement conditions described in the datasheet is set under the condition that RDS(ON) characteristics are almost flat. Use the gate voltage for this measurement condition as a reference.
When increasing the gate-source voltage VGS, VGS including surge voltage should be within the absolute maximum rating.

Please refer to the following documents for details on MOSFET gate-voltage.