If your toilet won't flush, a clog in the pipe is the most common cause. Attempt to dislodge the clog by flushing one time. Then, take a plunger and place it over the drain. Pump it vigorously to push the clog through.
If your bathtub or shower drain isn't working properly, you may be able to fish debris out using a drain cleaning tool. Many hardware stores sell plastic hooks designed to pull clogs out of the pipe. Please do not use corrosive chemicals to try to clean the drain.
You may also want to purchase drain catches to prevent this problem from reoccurring.