The inductor on the gate side of the power MOSFET transistor can be a ferrite bead or a few turns of wire wrapped around a 10 ohm, 1/4W resistor. The purpose of this inductor is to supress RF oscillation from the MOSFET.
This circuit can, in theory, switch a lot of current, an IRFZ34N MOSFET can handle over 35 Amps if connected to a proper heat sink. Inductive loads may require special care since they can generate large voltage spikes that can damage the MOSFET. Replacing the 1N4002 with a fast recovery diode may help absorb the reverse voltage kick when driving an inductive load such as a motor.
Note that the pwm control has an opposite effect on these two circuits, the low side version is on with a high pin 7 output voltage and the high side version is on with a low output.
In general, NMOS transistors like the IRFZ34N are lower cost and higher
current compared to PMOS transistors like the IRF9540. Almost any power MOSFET
transistor will work in these circuits, the load current should be lower than
the transistor's maximum rating.