What is the purpose if the feast of visitation and on what day of the year is it celebrated? Recently read a little mention of feasts the Catholic Church commemorate regarding events in Mary's life. Does the feast of visitation refer to the conception of Jesus?
The Visitation commemorates the event described in Luke 1:35-56, in which Mary goes in haste to her relative Elizabeth:


  39 In those days Mary arose and went with haste into the hill country, to a town in Judah, 40 and she entered the house of Zechariah and greeted Elizabeth. 41 And when Elizabeth heard the greeting of Mary, the baby leaped in her womb. And Elizabeth was filled with the Holy Spirit, 42 and she exclaimed with a loud cry, “Blessed are you among women, and blessed is the fruit of your womb! 43 And why is this granted to me that the mother of my Lord should come to me? 44 For behold, when the sound of your greeting came to my ears, the baby in my womb leaped for joy. 45 And blessed is she who believed that there would be a fulfillment of what was spoken to her from the Lord” (English Standard Version; the Magnificat immediately follows).


In the Catholic Church, it is celebrated on May 31. It is liturgically a feast, hence one notch below (so to speak) a solemnity. Since it is not feast of our Lord, it is not celebrated if it falls on a Sunday.