1.  The expression "kingdom," "kingdom of God," or "kingdom of Heaven"  is used in two main senses in the New Testament.

Heaven -Matthew 25:34; 2 Peter 1:11; Acts 14:22.

The church that Jesus built-Matthew 16:18-19; Colossians 1:13; Revelation 1:9

2.  Christ's kingdom or Church was established on the first Pentecost  after Christ's resurrection as is recorded in Acts 2.

It was to start in Jerusalem (Isaiah 2:1-3) in the last days of the Roman kings.( Dan. 2:44). 

John the Baptist preached that it was "at hand"  (Matthew 3:1-2).

The disciples were taught to pray for it to come  (Matthew 6:10).

It was to come in the same generation in which Christ preached  (Mark 9:1).

Joseph of Arimathea looked forward to it (Luke 23:50-51).

The disciples inquired about its coming (Acts 1:6-8)

THE KINGDOM CAME IN ACTS, CHAPTER 2

It was to come with power, Mark 9:1, and it did as the Holy Spirit came with power Acts 2:1-8. Therefore,  the kingdom / church came in Acts 2.  The kingdom is not spoken of as being in existence until the power came as the Holy Spirit in Acts.  Now we have as church into  which people are being baptized into, Acts 2:38-41, added there unto by Christ-Acts 2:47.  Now it, the kingdom, the church is spoken of as being in existence.  Acts 2:41, 47; Colossians 1:13;  Hebrews  12:28;  Romans 14:15-17, 16:16; Rev. 1:9

3.   The Church and the Kingdom are identical

They began at the same time (Pentecost) and the same place (Jerusalem).

They have the same:  

Head or King  -Christ.  
The same law -The law of Christ of the New Testament.  
The same territory  -All nations.  
The same subjects or citizens, Christians, baptized believers according to the doctrine of Christ through the Apostles Acts 2:38-47; Acts 8:12, 8:35-39, Acts 16:14-16, 30-33;  Galatians 3:26-29
The same process for entering the church is also for entering the kingdom. 

4. How You Can Become a Citizen in Christ's kingdom/church.

Hear the Gospel of Jesus Christ, the King and obey it.    Hebrews 5:8-9

Hearing is Faith listening....Romans 10:17.  The Gospel is the Death, Burial and Resurrection, according to 1 Corinthians 15:1-4.  Jesus tells us to preach the Gospel and when it is obeyed, to baptize the believers in the name of the Father, the Son and the Holy Spirit.  Matthew 28:19-20;  Mark 16:15-16;  Luke 24:46-48

Believe in Jesus Christ...John 8:24;  Hebrews 11:6;  John 12:48-49

Repent of sin...Acts 2:38;  Luke 13:3,5;  Acts 17:30-31

Confess Jesus Christ to be the Son of God  ... Acts 4:12;  Matthew 10:32

Be Baptized in Jesus Christ for the remission of Sin...Romans 6:3-6;  Acts 2:38; Galatians 3:26-29;  Acts 2:47.

Live a faithful Christian life..1 Corinthians  15:58;  2 Timothy 4:6-8; Revelations 2:10

CONCLUSION:  We urge you to continue to study the Word of God to ascertain the Salvation of the New Testament found only in the Kingdom of Christ.