In the absence of water or when unable to use water, one may instead of performing wudu or ghusl perform tayammum. This is stated in the Qur’an in verse 6, Chapter Al-Ma’idah which means:

“If you do not find water, then perform tayammum with the pure soil. Pass it onto your faces and arms”.
 
The Prophet peace be upon him said what means:

“The earth is made as a place for our prayers, and its soil is made for our purification” (Related by Imam Muslim).
 
One must make sure that the time of the prayer has set in before performing the tayammum. The tayammum is valid for one obligatory prayer only and for as many optional prayers as one wishes. However, one repeats the tayammum before each obligatory prayer.

How to perform Tayammum

One needs to make sure that the soil is pure, dusty (generates dust when hit unlike beach sand) and unused (has not been used before) before performing tayammum (figure-1-).
 
It is recommended to say Bissmillah. It is an obligation to strike the soil with your palms. In your heart, make the following intention: “I intend to perform tayammum to make performing the prayer permissible” while transferring the soil until it touches your face (figure-2-).
 
Pass the soil on all of your face (figure-3-)

Strike the soil again and pass it on both hands and forearms, including the elbows. It is recommended to pass it on the right arm first then the left (figure-4-). It is an obligation to make sure that the soil on the left palm reaches all the parts of the right arm and conversely (figure-5, figure-6, figure-7, figure-8).