If your toilet won't drain properly, use a plunger to attempt to restore normal function. As you pump the plunger, be careful not to flush the toilet, or you could cause the toilet to overflow and flood your bathroom.
Many household drains can also be cleared using a plunger. If your shower or sink drain regularly clogs, you may need to fish out any debris lodged in the pipes. Many hardware stores sell drain cleaning tools for a few dollars that can help. Do not use corrosive chemicals to clear your drain.