Button Cells find wide applications in small electronic devices such as watches, hearing aids and calculators. Button Cells have outputs at 1.5 volts and 3 volts. They provide very little power which is sufficient for small gadgets. 
Button Cells have a relatively long life. They are also safe enough to be used inside the human body in bio-medical devices.
They have a stable output voltage which does not drop even over long periods.
The Electrolyte used is Potassium Hydroxide (KOH) in paste form. The electrodes are Zinc (anode) and Silver (Cathode). Button cells are therefore safe for the environment.
Since silver is expensive, cost is one of the downsides of the button cell.
Coin cells are similar to button cells but they are larger in size. Coin cells are used in applications such as CMOS sets where more power is required.
The Anode is the outer container of the button cell while the cathode is the top layer of the battery.
Coin Cells can be used to power torchlights and other devices with relatively higher power consumption by connecting two or more cells in series.
Button Cells should be kept away from children who can accidentally swallow it.