How does one perform tayammum when water is unavailable or one is unable to use it?

The correct description of tayammum is for the person performing it to say "Bismillah" (In the name of Allah) while intending tayammum. Then, he strikes the surface of the earth once with his palms, after which he wipes the back of his right hand with the palm of his left hand, and the back of his left hand with the palm of his right hand. Following this, he wipes his face with both hands. This is then followed by the prescribed supplications after ablution. This is based on the narrations of the Hadith of Ammar ibn Yasir in Sahih al-Bukhari and other collections, which explicitly state that wiping the hands precedes wiping the face.