Pentecost Sunday is next week. Does your church mark it in any way? If so how?
(I was unaware of this until recently, apologies if it's old news, but I found it really helpful...)
Pentecost didn't begin in Acts. The coming of the Spirit on the early church is called Pentecost because it happened on the day of Pentecost. It was the Greek name for the Hebrew festival of Weeks (explaining why Jerusalem was so busy with visitors). The Festival of Weeks celebrated the giving of the Law to the people of Israel on Mount Sinai, and was 50 days from God's redemptive work of the Exodus. It marked the beginning of the Mosiac (Old) covenant. For a long time the Jewish people expected that the promised new covenant would be given on Pentecost.
So Luke higlights the events of Acts 2 as happening specifically on the day of Pentecost, because the giving of the Spirit began the New Covenant, 50 days after Jesus redemptive work over sin and death. The Spirit is for us what the Law was for Judaism.