The Acts of the Apostles is a book of the Bible, which now stands fifth in the New Testament. It is commonly referred to as simply Acts.
Acts tells the story of the Early Christian church, with particular emphasis on the ministry of the Twelve Apostles and of Paul of Tarsus. The early chapters, set in Jerusalem, discuss Jesus's Resurrection, his Ascension, the Day of Pentecost, and the start of the Twelve Apostles' ministry. The later chapters discuss Paul's conversion, his ministry, and finally his arrest and imprisonment and trip to Rome.
It is almost universally agreed that the author of Acts also wrote the Gospel of Luke. The traditional view is that both books were written c. 60, though most scholars, believing the Gospel to be dependent (at least) on Mark's gospel, view the book(s) as having been written at a later date, sometime between 70 and 100.