Achamana is a body purification process using a small quantity of water. Achamanam patra (Copper glass, copper spoon, and copper plate) is used to perform this. Achamanam is done before starting any kind of puja or anushatana or japa.
There are 3+15 = 18 mantras for which Achamana is to be performed. For first three times, water is to be sipped in by chanting the beeja mantra of Kali. Before sipping, you have to take the water in right hand, chant the mantra and then sip it. This is for purification of mind and other internal organs. For rest of the mantras, chant the mantra and then touch different parts specified here with fingers (middle and ring finger) after wetting them water.