Assuming you are referring to a drain in your bathroom sink, there are a few ways you can clean it. First, you can use a plunger to try and dislodge any debris that may be caught in the drain. If that doesn't work, you can try using a drain snake. If neither of those methods work, you may need to remove the drain cover and clean it out manually.
To clean the drain cover, you will need to remove it and then soak it in a mixture of vinegar and water. Once it has soaked for a while, scrub it with a brush to remove any build-up. Once the cover is clean, you can replace it and run some hot water down the drain to flush it out.