This verse refers to the night of Jacob's wedding to Rachel. However, Laban, Rachel's father, tricked Jacob by substituting Leah, Rachel's older sister, for Rachel in the bridal tent.

"In the evening, he took Leah his daughter, and brought her to him": This means that Laban brought Leah to Jacob in the darkness of the night. The traditional wedding custom at the time involved the bride being heavily veiled.
"He went in to her": This is a euphemism for sexual intercourse. Jacob consummated the marriage with Leah, believing her to be Rachel.

This deception was part of Laban's scheme to ensure that his older daughter, Leah, was married before his younger daughter, Rachel, as it was custom that the eldest daughter must be married first. Jacob had worked seven years for Rachel, but Laban manipulated the situation for his own gain, forcing Jacob to work another seven years to finally marry Rachel.