If your toilet isn't flushing, locate a plunger and push it into place over the drain. Move the plunger up and down to dislodge anything stuck in the pipes. If you are successful, the water will drain after you break the suction. Repeat the process as many times as necessary.
If water isn't draining properly in your sink or shower, many hardware stores sell drain cleaning tools and products to dissolve drain clogs. Please avoid corrosive chemicals that could hurt the plumbing system.
Consider installing drain traps to prevent future reoccurrences.