The Spirit comes on all of them (not just the 12 apostles) and they start talking in the native languages of the Jews gathered from those places, amazing them. To Jews it sounds like gibberish, like they are all drunk (Eli made the same mistake - 1 Samuel 1:14). Peter as spokesman for the apostles explains that Joel 2 has been fulfilled. They killed Jesus, as God planned. God proved Jesus was from Him with many signs, and now He raised Him back to life. David predicted this, and wasn't talking about Himself, since he is still dead and buried in this city. We saw Jesus alive again, and ascend to heaven, and now Jesus has poured out the Spirit as you just saw happen. He is the Lord and the Christ.
Many are convicted, believe and are baptized. The growing group follow the apostles' teaching, see miracles done by the apostles to prove the God-given-ness of this, give generously for those in need among them, extend hospitality, and go to temple frequently together to worship God.
How this is about Jesus
Just because He is ascend and not visibly with the disciples, doesn't mean He isn't working anymore. Pentecost is an act of Jesus. He sent the Spirit (Acts 2:33) to testify about Himself to the nations (verses 22-24, 31-33, 36).
- There are times of waiting in our lives, like the 10 days from ascension to Pentecost for the disciples. The best thing for us to do is surround ourselves with God's people in worship and fellowship (Acts 2:1; Luke 24:53).
- The Spirit doesn't encourage us by showing us miracles or giving us amazing experiences, but by pointing us to Jesus, equipping us to testify to Him, making us seek Him in worship, and be generous and loving with others.