Turning high side MOSFETs on and off (assuming you use an n-channel MOSFET to achieve fast switching due to their low RDS(on)) require bootstrap circuit to boost the gate voltage higher than the source voltage. We achieve this by utilizing a boostrap capacitor, diode and a BJT transistor.

Schematic and the Working Principle:

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In the inital state, the BJT is turned on. The gate of the high side MOSFET is at 0V. Bootstrap capacitor charges to VCC through the diode. The load is connected to ground, so the source of the MOSFET is at ground potential.

When the BJT is turned off, capacitor discharges to the gate through the 1k resistor and turns the MOSFET on and we get 12V at the source terminal. Since the capacitor and the source terminal are connected, we get a total of 24V at the gate terminal which turns the MOSFET fully on.