The Catechism in Questions & Answers

210. How did the outpouring of the Holy Spirit occur?

The Bible relates the following: “When the Day of Pentecost had fully come, they were all with one accord in one place. And suddenly there came a sound from heaven, as of a rushing mighty wind, and it filled the whole house where they were sitting. Then there appeared to them divided tongues, as of fire, and one sat upon each of them. And they were all filled with the Holy Spirit” (Acts 2: 1-4).
The Holy Spirit filled the Apostles and all those who were with them as an enduring gift, as power from on high (cf. Luke 24: 49).