O God, come to my assistance
Traditional opening to the Rosary from Psalm 70:2, as on the Holy See's Rosary page.
Source: The Holy See, How to pray the Rosary
Psalm 70
O God, come to my aid. O Lord, make haste to help me.
V. stands for versicle (leader). R. stands for response (congregation). If praying alone, say both parts yourself.