How to interpret Vgs(th) min/max in a MOSFET datasheet?
This means that the threshold voltage between the Gate and Source is between -2V and -4V, meaning the Gate must be between 2-4V lower than the Source in order for it to be in it's 'on' state.

The third column on your screenshot is the test conditions, as it says in the datasheet. If you are doing a switching circuit, just make it a nice 5V circuit, that way you are more than covered, stick a pull-down or pull-up resistor on the gate and switch the 5V to turn it on and off. 

Being above the maximum, you can be sure that this way, the MOSFET will be turning fully on and off each time it is switched.