The answer to 'how to unclog P-trap' is to use a plunger or a plumber's snake to clear the clog. First, try using a plunger to dislodge the blockage. Plunge the drain vigorously up and down several times. If that doesn't work, use a plumber's snake or auger to reach deeper into the pipe and break up the clog. Carefully insert the snake into the drain and turn the handle to extend the cable, working it back and forth to clear the obstruction.
If the clog persists, you may need to disassemble the P-trap under the sink to access and clear the blockage. This involves unscrewing the slip nuts that hold the trap in place, removing the trap, and using a wire or other tool to dislodge any debris. Be sure to have a bucket or rag on hand to catch any water that drains out. Once the clog is cleared, reassemble the P-trap and run water to ensure the drain is flowing freely.