What about why and how?
Yes!
WHAT ? Jesus said He'd BAPTIZE His followers with the Holy Spirit ( Luke 24.49, Acts 1.5, 8 ) plus John promised same thing ( Matt. 3.11 ) = the Spirit coming UPON Believer, which doesn't mean IN them. The INDWELLING of Holy Spirit happens at salvation ( Jn 4.14 ) ... the Baptism occurs AFTER the person is Born Again.
WHEN ? The 10 disciples ( 12 less Judas and Thomas ) on evening following Resurrection were Born Again that night = Holy Spirit IN them ( John 20.22 ). So then the 12 disciples ( 11 + new Matthias ) and/or 120 ... were Baptized WITH the Holy Spirit at Pentecost ( Acts 2:3-4 ).
WHERE ? For the 120 it was in the Upper Room. For the 3000 Jews in Jerusalem ... somewhere near the Upper Room ??? For Cornelius and his house ... in his house ( Acts 10 ) ??? For the Ephesian ... was it their house or outside ( Acts 19 ) ???
Regarless. Baptism in Holy Spirit is a 2nd manifestation of HS and always follows Believers salvation ( HS in them ). HS baptism can happen within seconds/minutes after person really believes ... example Cornelius and house. Or later, as in the case of the Samaritans ( Acts 8 ). Now when the apostles who were at Jerusalem heard that Samaria had
received the word of God ( terminology = Born Again ) , they sent Peter and John to them, who, when they had come down, prayed for them that they
might receive the Holy Spirit [ conclusion, terminology implies THE BAPTISM ] ( Acts 8.14 - 15 ). Peter/John knew they were born again ... they why pray for Holy Spirit ? Because, they were praying for the SECOND manifestation = the Baptism !