I have heard more than a few people say today that they wish the modern day church was more like the first churches after the time of Jesus. There are passages that talk about how wonderfully unified, supportive, nurturing, etc that the church was back then. But then there are other stories such as that of the churches in ancient Corinth.
Paul had visited Corinth on one of his missionary journeys (he was one of the founders of the church there) and had been there for an extended period before moving onto Ephesus. The first letter is dated to somewhere in the 50-55 CE timeframe and was likely written while Paul was in Ephesus.
The second letter is a bit more difficult however to pin down. The general consensus is that, like the first letter, 2 Corinthians was definitely written by Paul but it is thought that it is actually a combination of two or more letters that Paul sent. There are references in the letter to a message he had received from the church and there are several places where the tone/subject/focus of the letter changes very abruptly which is not usual for Paul’s other letters.
The general focus of both of the letters is on Paul trying to help the Corinthian believers through several very specific and significant issues they were facing. There were issues of immoral practices taking place, issues of division and conflict, issues of understanding of what we now refer to as the Lord’s Supper, and more. Paul seems to be responding to many of these in turn to help them with getting back on track.
As a result, there is a great deal of these letters that can be brought to bear on situations that the church faces today. How to reach across boundaries, how to assure inclusion and welcome, and how to stay on track in faith.
You can find more about these letters in this excellent summary at Bible Gateway