The answer to 'how to unclog drain' is to first try a plunger or a drain snake/auger. If that doesn't work, you can try using a drain cleaner product or baking soda and vinegar. If the clog persists, you may need to remove the drain pipe and clear the blockage manually. Always wear gloves and safety goggles when working on drains, and consider calling a professional plumber if you're not comfortable tackling the job yourself.
Regularly maintaining your drains by pouring a baking soda and vinegar solution down them every few months can help prevent future clogs. But if you encounter a stubborn clog that won't clear, it's best to call in a professional plumber to properly diagnose and fix the issue.