You can unclog a drain manually using a plunger or snake, naturally with baking soda and vinegar, or with chemical drain cleaners for fast action. Your method of unclogging depends on the severity of the blockage and the age of your pipes.
First, run two to three inches of water over the drain hole, then take a plunger and apply petroleum jelly around the rim to help it form a tighter seal. Place the plunger over the drain, then force the plunger hole down repeatedly for a few minutes; ideally, the water pushes obstructions out of the way, unclogging the drain.
If plunging does not work, take a snake, remove the trap of the drain hole and insert the snake until you meet the obstruction. Hook the end of the snake solidly into the debris and either push it around to loosen and disintegrate the obstruction or pull it out of the drain entirely. Be careful not to push it further into the pipes. Pour boiling hot water down the drain when done.
If the obstruction remains, pouring in a chemical drain cleaner that contains sulfuric acid or lye, or using a natural variant made of baking soda and vinegar, may help dissolve it.