What does Va'yechulu mean literally in Hebrew? What is the function of Va'yechulu during worship?
It's the first word of Genesis 2:1. Genesis 2:1–3 is recited a few times a week in the liturgy, perhaps most notably toward the end of the evening synagogue services on Friday nights: many congregations recite the passage aloud and in unison on that occasion. If you saw a reference to "Va'yechulu", it likely meant that passage and may well have meant that recitation of it.