With all the stuff that typically goes down a bathroom sink drain -- soap suds, toothpaste, shaving cream, face creams, makeup, hair and whiskers, for example -- it's no surprise that it gets stopped up from time to time. When your sink runs slow, or stops flowing completely, you need to remove the drain stopper to reach the clog. You'll also need to remove the drain stopper if it needs to be replaced.
Look underneath the sink to the pipe at the bottom of the sink. This is the tailpiece. Look behind the drain tailpiece pipe. You may need to use a flashlight to see. You'll see a round, shiny chrome nut. Attached to the nut is the stopper control rod.
Grab the edge of the nut firmly with your fingers. Turn the nut clockwise looking at it from the front of the sink.
Loosen the nut all the way to get the sink drain stopper out. Grab the stopper control rod and pull it out of the drain tailpiece pipe.
Reach into the sink from the top and pull the sink drainer stopper up and out.
Lie down on your back and stick your head underneath the sink if you can't reach the nut by just reaching in.
The nut you need to loosen to remove the sink drainer stopper doesn't look like an ordinary nut. It has ridges on it. These ridges allow you to turn it with your fingers. If you are unable to loosen it, use a pair of pliers.