What is the aim of 100ohm resistor between the micro-controller pin and the gate of the N-channel MOSFET?
The 100 Ohm resistor on the gate of the N-Channel MOSFET is there to stop any potential ringing. Ringing is caused by gate capacitance in series with the inductance of the track/wire.
The 10k resistor is just a pull-up resistor to keep the gate of the P-Channel MOSFET high. Or so I assume as you haven't actually labelled the nodes of the P-Channel. Once the MCU pin goes high, the N-Channel MOSFET turns on, which pulls the gate of the P-Channel MOSFET low, turning it on and allowing current to flow through it.