The passage is actually Psalms 13, not 12. Here is the summary:
David cries out to God, asking how long he will be forgotten and his enemies exalted over him. He asks God to look upon him and enlighten his eyes, lest he fall asleep in death and his enemies prevail. Despite his troubles, David hopes in God's mercy and trusts that he will be saved, and he vows to sing psalms to God's name.
1 Unto the end. A Psalm of David. How long, O Lord? Will you forget me until the end? How long will you turn your face away from me 2 How long can I take counsel in my soul, sorrowing in my heart throughout the day 3 How long will my enemy be exalted over me 4 Look upon me and listen to me, O Lord my God. Enlighten my eyes, lest I fall asleep forever in death 5 lest at any time my enemy may say, "I have prevailed against him." Those who trouble me will exult, if I have been disturbed 6 But I have hoped in your mercy. My heart will exult in your salvation. I will sing to the Lord, who assigns good things to me. And I will sing psalms to the name of the Lord Most High