They saw something like flames of fire that were separated and stood over each person there. They were all filled with the Holy Spirit, and they began to speak different languages by the power the Holy Spirit was giving them. The Wind's beginning to blow. The Heavenly Power is descending on the believers. The Holy Spirit baptizes them with His powerful Presence.
Supernatural abilities flow into the disciples.
And as the rest of this chapter describes, people from all over the world hear the Gospel and in confession and repentance for their sins, they accept Jesus as Lord and Savior. 3,000 people are baptized on that day alone. And the book of Acts goes on to describe the church lifting off and circumnavigating the whole world with God's message. Thousands and thousands and thousands join the church and it becomes a global movement for God. Depend on Him.