What you are missing in the day of Pentecost that you referred to is who the Holy Ghost fell on, why, or the origin of that occurrence.
First of all, there it fell on the apostles in a miraculous fashion. For the origin, one must go back to what John the Baptist said as recorded in Luke 3:16, (baptsm with fire), and what Jesus told the apostles as recorded in Luke 24:49; to tarry in Jerusalem until they received power from on high. This is what occurred in Acts 2. The apostles received the power from on high and THEY spoke with tongues as a sign to the Jews as noted in the Acts 2 text, who then believed and were converted also as noted in the text in Acts 2:38-47, and became the church at Jerusalem. The similar thing happened in Acts 10 except the Holy Ghost first fell on the Gentiles as a sign of heavenly approval, and they then were baptized into Christ and became the first of the Gentiles converted in Caesarea and the starting of the church there. Note all other instances of the miraculous gifts via the Holy Ghost was the result of the laying on of the apostle's hands. Acts 2 was the power from on high meant for the apostles.
I hope this helps.
Here in Acts 2:38, we read about Jewish Christians. For them, the order was:
1. Repentance.
2. Water baptism.
3. Reception of the Holy Spirit.
The conversion of Samaritans is recorded in Acts 8:14-17. There we read that the following events occurred:
1. They believed.
2. They were baptized in water.
3. The apostles prayed for them.
4. The apostles laid their hands on them.
5. They received the Holy Spirit.
In Acts 10:44-48 the conversion of Gentiles is in view. Notice the order here:
1. Faith.
2. The indwelling of Christ. (Revelation 3:20).
3. Water baptism.
(The gifts of the Holy Spirit, speaking in tongues, healing, prophesy etc. are given later to those who seek them)
Acts 19:1-7 A group of believers in Ephesus.
1. They believed.
2. They were rebaptized in water.
3. The Apostle Paul laid his hands on them.
4. They received the Holy Spirit.
"Does this mean there were four ways of salvation in the Book of Acts? Of course not. Salvation was, is, and always will be on the basis of faith in the Lord. But during the transition period recorded in Acts, God chose to vary the events connected with the reception of the Holy Spirit for reasons He knew but did not choose to reveal to us." (Believers Bible)
.