The church started in Jerusalem at Pentecost when the Holy Spirit empowered the apostles to preach Christ.  But what started in Israel was only the beginning as Jesus mobilised them in global mission (Acts 1:8).  After the persecution which followed Stephen's murder, many believers moved out of the city; some, including Philip the Evangelist, went to Samaria (Acts 8:1-5).  When he preached the gospel there, many people responded with joy (Acts 8:6-8).

The apostles agreed to send Peter and John to see what the Lord was doing in Samaria.  They would have remembered when Jesus had taken them through Samaria to meet a woman at Sychar (John 4:4-7), and many in that town believed in Jesus (John 4:39-42).  When Peter and John arrived, they met people who had believed the gospel and had been baptised into the Name of Jesus.  But the new Christians had not yet been taught to welcome the Holy Spirit, when they repented and trusted Jesus.  

After His resurrection, the Lord Jesus had told the apostles that they must receive the Holy Spirit who would be sent to them (John 20:22).  In that way, although they did not understand it at the time, they had been prepared for Pentecost. But Philip the Evangelist was not present on that occasion.  Presumably he was one of the Pentecost converts, and known to be full of the Holy Spirit (Acts 6:3-5), but he did not teach new believers to actively welcome the Spirit.  So, Peter and John, laid hands on the Samaritan believers assuring them that they should welcome God's Spirit, as equal brothers and sisters to the believers in Jerusalem.

When you share the gospel, tell people about Jesus who died for their sins and was raised to make them right with God.  When you do, they often need to be taught how to respond: believe in Jesus, repent of sinful rebellion, be baptised and welcome His Holy Spirit (Acts 2:38).  Do not think you cannot help them; indeed, you may well be the person the Spirit has chosen to lead them to Christ (www.crosscheck.org.uk).