"Acts 1"

The book of Acts picks up where the Gospel of Luke left off, and is written by the same person Luke to same person he wrote of Luke to Theophilus.

Acts chapter 1 is composed of an introduction, resurrection-ministry of Christ, the apostolic commission that's also in the Gospels, promise of Christ's second coming, the instructions of waiting for the spirit in 10 days, and choice of Matthias.

Christ's disciples are making a transition from being with Christ on earth to ministering to others without Christ on earth. That is seen in beginning of Acts 1, and Luke gives a brief introduction to Theophilus.

Introduction ( verses 1 and 2)
In verse 1 Luke addresses his friend Theophilus, and verse 2 Luke explains why he wrote the book of Acts to him. Until that day in which He was taken up-this statement refers to Christ's resurrection, after that he through the Holy Ghost had given commandments unto the apostles whom he had chosen:- this statement of Christ is about day of pentecost, and Great commission that's written in all 4 gospels.
One of the things the book of Acts is about is the early Christian church, and it was written around the same time that Luke was around 65 AD. So that time was over 30 years after Christ ascended into heaven, and book of Acts is how the early church grew.

The Resurrection-ministry of Christ ( verses 3 through 7)
These verses are about Christ's time with his disciples after the resurrection, and in verse 3 it states that Christ was with them for 40 days. He was speaking to them things pertaining to the kingdom of God, and He also instructed them not to depart from Jerusalem until the Holy Ghost came upon them.
His disciples asked him when will the time be for the kingdom to be restore to Israel, and in verse 7 he answered them that it was not for them to know. Only His Father knows.

The Apostolic Commission and promise of Christ's return to earth ( verses 8 through 11)
After Christ told his disciples only the Father knows when His kingdom will be restore to Israel he gave them the Great Commission ( Matthew 28:18-20, Mark 16:15-18, Luke 24: 47,48, and John 20:21-23), and after they receive power of the Holy Ghost they will be witnesses to Jerusalem, Judaea, Samaria, and to the uttermost parts of the earth. And in verse 9 it states Christ was telling them these things while ascending into heaven.

While he was no longer seen in the sky His disciples were still looking up toward heaven for Him, and two men in white apparel first asked them why ye men of Galilee are still looking up into heaven, than they told them that same Christ they saw ascend into heaven shall also return to earth. This refers to Christ second coming.

This took place around Mount Olivet, because in verse 12 it states men of Galilee were returning to Jerusalem that was a Sabbath's day journey.

The 10 days' waiting for the Spirit, and the choice of Matthias ( verses 12 through 26)
After men of Galilee returned from Mount Olivet to Jerusalem they came into the upper room that included the 11 apostles, the women that witness Jesus' resurrection, and Jesus' mother Mary with His brethren. They were all in one accord in prayer, and supplication.
In verse 15 we read that there were 120 of them in that upper room, and Peter stood up in the midst of them to begin the process of replacing Judas. Starting to prophecy David that refers to Judas Peter decides that the replacement must have been with Jesus from time of baptism until His resurrection, and it came down to 2 men. It came down to Justus, and Matthias. They casted lots, and it fell on Matthias for him to be Judas replacement.

Recapping Acts 1
Acts 1 verses 3 through 9 continues with Luke 24:46-53, and Acts 1 verse 13 in where they are in the upper room picks up where Luke 24:52 left off in where they return to Jerusalem with great joy. Acts 1 was pretty much a continuation of Luke to where that Gospel goes from the birth of John the Baptist to Christ's ascension to heaven, and Acts 1 explains what, and where the disciples went to after Christ's ascension.
Before they return to Jerusalem they were given instructions from Christ to wait for the Holy Ghost, than put the Great Commission to affect into first Jerusalem, Judaea, Samaria, than rest of the world. Between Christ's ascension to heaven to the promise of the Holy Ghost 120 of His disciples that included his 11 apostles were all in 1 accord in prayer, and supplication in the Upper Room. With Peter leading them they also replaced Judas with Matthias.
After Christ's resurrection He was with them for forty days talking about His Kingdom, promising them the Holy Ghost, and giving them the Great Commission while ascending into heaven.