First and foremost, you must determine the cause of the clog before attempting to fix it. It is most often caused by soap and hair. If you're unsure of what caused the clog, you can try boiling water and pouring it down the drain in small bursts. If you're not successful with this method, you may need to repeat the procedure until the blockage is removed.
To unclog a drain, you may use an electric snake or a manual hand snake. To use the snake, cut a length of cable and twist it around the clog. You should use a trash can near the drain so that you don't splatter goop. If you don't have the right tools for this job, you can also try a homemade declogging solution or chemical agent.
If you still can't unclog the drain, you can use vinegar and baking soda to dissolve the hair & mineral sludge that's clogging it. You can also add some vinegar and leave it for a few minutes to see if it works. When using this solution, make sure not to use excessive force or you might damage the pipes and fixtures. You may need to call a plumber to fix your flooded bathroom or kitchen sink.