A kettle is used for heating water. In earlier times, it was made out of metal and put onto a heat source (fire, stovetop). Nowadays it is almost entirely displaced by the electric kettle, which is commonly made out of plastic and contains a metal heating plate or spiral on the inside.
A teapot is a ceramic pitcher where you put the boiling water and tea leaves to brew the tea.
Do you mean the Utah Teapot?