What is the method for the intention of the heart, and is mere knowledge of the act to be performed sufficient?

"Niyyah (definition)" (intention) is the aim and determination of the heart to perform something without hesitation; it is not mere desire. So, whoever intends to do something has made an intention for it, and it does not require effort or vocalization within oneself. For example, if someone stands up for prayer intending to pray Asr, their intention is realized. Similarly, if someone uses water with the intention of performing ablution (Wudu') or ritual bathing (Ghusl (definition)), the intention is achieved.