Pmos has gate referenced to source terminal (source of current because it's a P device). This means the more positive terminal.
(N device is different since its gate is referenced to the more negative terminal.)
To shut off a P device, apply same voltage as source. Generally this means the positive supply voltage. A 10k resistor attached from gate to Supply+ is a handy way to do this job.
To turn on a P device fully, connect gate to 0V ground (in simple terms).
It gets complicated because the gate can be perforated if exposed to high voltage (high potential). Your biasing method must be designed in consideration of this.
