Sotah 38 - How to bless
Every day the Kohanim (Priests) should bless the people and say to them, "May God bless you and keep watch over you. May God make His presence enlighten you and grant you grace. May God direct His providence toward you and grant you peace."
Outside the Temple, they say these three phrases, and the people answer "Amen" to each one. They also say the Name of God not as it is written, but using a changed form called "Adnut" and denoting ruler or master.
In the Temple they said the blessing as one long phrase, without an interruption for "Amen." In the Temple people as a rule did not say Amen, but responded with a longer phrase; here this phrase would interrupt the blessing. Moreover, in the Temple the Priests pronounced the Name of God as it it is written, in the form that implies "was, is and will be." The exact pronunciation of it is not known today.
Art: Jacob Blessing the Children of Joseph by Rembrandt Van Rijn