This prayer is traditionally said three times a day, and it is a distinctly Catholic practice. Many years ago, it was common for village church bells to ring at 6:00 a.m., noon, and 6:00 p.m. each and every day, to remind the faithful to pray the Angelus. (Those times also corresponded with going to work, breaking for lunch, and ending the work day to go home at night.) The praying of the Angelus is a devotion in memory of the Incarnation, when God the Son was miraculously conceived in Mary's womb and became flesh.
The Angelus gets its name from the opening words of the Latin form: "Angelus Domini nuntiavit Mariae" ("the Angel of the Lord declared to Mary").
The Angel of the Lord declared to Mary: And she conceived of the Holy Spirit. Hail Mary, full of grace, the Lord is with thee; blessed art thou among women and blessed is the fruit of thy womb, Jesus. Holy Mary, Mother of God, pray for us sinners, now and at the hour of our death. Amen.
Behold the handmaid of the Lord: Be it done unto me according to Thy word. Hail Mary...
And the Word was made Flesh: And dwelt among us. Hail Mary...
Pray for us, O Holy Mother of God, that we may be made worthy of the promises of Christ.
Let us pray: Pour forth, we beseech Thee, O Lord, Thy grace into our hearts; that we, to whom the Incarnation of Christ, Thy Son, was made known by the message of the angel, may by His Passion and Cross be brought to the glory of His Resurrection, through the same Christ Our Lord. Amen.
I think most of us who grew up in a post-Vatican II world have probably never even heard of the Angelus. For my part, I've heard of it--I've seen it mentioned in books--but I've never prayed it. In our busy world today, it's hard to imagine all Catholics stopping what they're doing three times a day to pray when they hear the sound of church bells ringing. But it would probably be a better world if we did.