Acts 2:1-13

When the day of Pentecost came, they were all together in one place. Suddenly a sound like the blowing of a violent wind came from heaven and filled the whole house where they were sitting. They saw what seemed to be tongues of fire that separated and came to rest on each of them. All of them were filled with the Holy Spirit and began to speak in other tongues as the Spirit enabled them.
Now there were staying in Jerusalem God-fearing Jews from every nation under heaven. When they heard this sound, a crowd came together in bewilderment, because each one heard them speaking in his own language. Utterly amazed, they asked: "Are not all these men who are speaking Galileans? Then how is it that each of us hears them in his own native language? Parthians, Medes and Elamites; residents of Mesopotamia, Judea and Cappadocia, Pontus and Asia, Phrygia and Pamphylia, Egypt and the parts of Libya near Cyrene; visitors from Rome (both Jews and converts to Judaism); Cretans and Arabs-we hear them declaring the wonders of God in our own tongues!" Amazed and perplexed, they asked one another, "What does this mean?"
Some, however, made fun of them and said, "They have had too much wine."

Pentecost is the 50th day after the Sabbath of Passover Week. It is also called the Feast of Weeks, the Feast of Harvest and the day of first fruits. Passover is sometime in April, so you're looking at sometime in June for Pentecost.

The speaking of tongues they are talking about is explained further below when they say that each individual person hears them speaking in their own native tongue. And it was the Holy Spirit that let that happen. I think it's funny that so many people find it amazing that they are speaking in different languages and then the last verse says that some thought they were just drunk. Kind of like today, some people are amazed at what God does and other people just blow it off as coincedence or whatever.