There are several ways to clear an obstructed drain.  It can vary from clog to clog, but most of these techniques will clear your clog no problem.

The first thing you should try should be the home remedy techniques for fixing a clog.  Home techniques are:

- Plunger
- Wire hanger
- Liquid Drano cleaner

If those methods do not work its time to get some assistance.  If you can get your hands on a plumbers snake, they work well for clogged drains that are further down the pipe and out of reach of the hanger.  If your drain is still backed up after that, then its time to fork up some money for a professional plumber.  This is always a last resort as most drains can be unclogged relitively easily.  You just have to give a little effort.