The answer to 'how to unclog sink' is to first try using a plunger to dislodge the clog. Fill the sink about 1/3 full with water, place the plunger over the drain, and plunge up and down vigorously 10-15 times. If that doesn't work, you can try using a sink snake or drain auger to physically break up the clog.
If the clog is still not cleared, you may need to disassemble the drain pipe under the sink to remove the blockage. This is a more involved process that requires some plumbing skills, so it's often best to call a professional plumber if the basic methods don't work.