Driving 5V mosfet with 5V tolerant pins on 3.3V dsPIC33F
simulate this circuit &ndash; Schematic created using CircuitLab

R1 is a pull up resistor which you provide. M1 is the transistor within the PIC and the drain is internally not connected (thus open drain).

You need to choose R1 and the size will depend on how fast you need to switch your device on and off. A higher value resistor will lead to slower transition times (in particular output rise time). There will be a time constant formed by the resistor and the gate capacitance of your MOSFET. I suggest simulating as the choice of resistor is highly implementation dependent.

A typical good start for R1 in general purpose switching control is 10k.

To drive the pin high, set the pin to be an open drain output (as indicated in the text you have - the specifics will be in the reference manual) and write a '1' to that register bit.

What voltages are permitted at the pin will be in the device data sheet; you could simply bring up the 5V behind the 3.3V. A 5V tolerant pin will be 5V tolerant for input or output. Most microcontrollers have the pins set to inputs at reset.