Prior to entering Salaat (prayer), the person is required to undertake a certain purification procedure known as "Wudu" without which, the person's prayer would not be acceptable in the sight of Allah (SWT).
Ghusl is bathing the whole body with water. You must clean your body from any impurities, if any. Make the Niyyah (intention) in your heart that this act of Ghusl is for the purpose of preparing for Salah.
In Arabic, the word Tayammum literally means an 'aim' or 'purpose.' In Islamic Law, it refers to: 'Aiming for or seeking soil to wipe one's face and hands with the intention of purification and preparing oneself to pray, and so on."