It is believed that it is sometime during Paul's year-and-a-half long stay in Corinth that he writes to the church in Thessalonica. We had just a short paragraph about his journey through that city on his second journey, and in this letter, Paul just seems to be following up with them to see how they are doing and give them further instruction. I'll try to give you the general flow of this letter as well, but again, will be unable to do so without including some of Paul's own words...
Paul starts out his letter as he often does many of his letters, thanking God and praising Him for the faith of those to whom he is writing. Paul reminds the Thessalonians of his time with them, and how he lived among them. He reminds them that he was not trying to burden them or make anything difficult for them, but rather he tried to live as an example for them.
Paul talks about wanting to visit them numerous times since, but he had been unable to do so. Finally, he sent Timothy to them to strengthen and encourage them, and Paul says that he was comforted by a good report that Timothy brought back to him about them.
Next Paul goes into the teaching portion of the letter, if you will, reminding htem of how they've been taught to live, and he encourages them to do so even more. "It is God's will that you should be sanctified: that you should avoid sexual immorality; that each of you should learn to control his own body in a way that is holy and honorable, not in passionate lust like the heathen, who do not know God; and that in this matter no one should wrong his brother or take advantage of him."
Paul says he knows that he does not need to write to them about brotherly love, for he knows they are practicing it. But he continues his teachings with, "Make it your ambition to lead a quiet life, to mind your own business and to work with your hands, just as we told you, so that your daily life may win the respect of outsiders and so that you will not be dependent upon anybody."
Paul follows up these instructions with some specific information about the resurrection and the coming of the Lord. Kind of makes one wonder if they specifically asked about this subject, or why else Paul might've chosen to write to them about it. Regardless, he says, "Brothers, we do not want you to be ignorant about those who fall asleep, or to grieve like the rest of men, who have no hope. We believe that Jesus died and rose again and so we believe that God will bring with Jesus those who have fallen asleep in him. According to the Lord's own word, we tell you that we who are still alive, who are left till the coming of the Lord, will certainly not precede those who have fallen asleep. For the Lord himself will come down from heaven, with a loud command, with the voice of the archangel and with the trumpet call of God, and the dead in Christ will rise first. After that, we who are still alive and are left will be caught up together with them in the clouds to meet the Lord in the air. And so we will be with the Lord forever. Therefore encourage each other with these words...But you, brothers, are not in darkness so that this day should surprise you like a thief. You are all sons of the light and sons of the day. We do not belong to the night or to the darkness...But since we belong to the day, let us be self-controlled, putting on faith and love as a breastplate, and the hope of salvation as a helmet. For God did not appoint us to suffer wrath but to receive salvation through our Lord Jesus Christ. He died for us so that, whether we are awake or asleep, we may live together with him. Therefore encourage one another and build each other up, just as in fact you are doing."
Paul ends his letter with some final instructions about how they should live: "Respect those who work hard among you, who are over you in the Lord...Live in peace with each other...warn those who are idle, encourage the timid, help the weak, be patient with everyone. Make sure that nobody pays back wrong for wrong, but always try to be kind to each other and to everyone else. Be joyful always; pray continually; give thanks in all circumstances, for this is God's will for you in Christ Jesus. Do not put out the Spirit's fire; do not treat prophecies with contempt. Test everything. Hold on to the good. Avoid every kind of evil."
Some really good advice there, among which is one of my favorites: Pray continually.