The answer to 'how to unclog drain' is to first try using a plunger or a drain snake to clear the clog. If those methods don't work, you can try using a chemical drain cleaner, but be sure to follow the instructions carefully and ventilate the area. If the clog persists, you may need to disassemble the drain pipe to remove the blockage. This is a more complex task that may require the help of a professional plumber.
It's important to address a clogged drain promptly, as a blocked drain can lead to water damage and other plumbing issues. Regular maintenance, such as using a drain cover and cleaning the drain periodically, can help prevent clogs from forming in the first place.