What is preterism? What does a preterist believe?
Eschatology is a study of the end times. Things like the Book of Revelation, the rapture, and the great tribulation are among a few of the things that fall under eschatology. One example of the end time views is Preterism. Preterism is the Christian view that some or most of the prophecies of the Bible are placed as events which have already happened. Of course, Jesus’ return has not happened yet, but the most common view in eschatology used to be Historicism, which holds that the fall of Rome, the tyranny of the popes, the advance of Islam, and the rise of the Enlightenment were all predicted in the book of Revelation, however, this approach has largely been abandoned. Yet another view in the eschatological school is that of Futurism, and today, that’s what most believers hold too. Futurism concerns events immediately prior to the final return of Jesus Christ, and which they believe is spoken about by Jesus in Matthew 24, including the great tribulation, the rapture, and other things yet to come. These are all different views of the end times which all fall under the study of eschatology. 
A great number of believers, in fact a majority of Christians, believe in the rapture. Some believe we will not have to do through it; some believe we’ll be raptured out mid-way through the Tribulation (mid-tribbers), and yet others believe Christians will go through the entire great tribulation where God’s wrath is poured out on the world, however, the Apostle Paul wrote, “For God has not destined us for wrath, but to obtain salvation through our Lord Jesus Christ” (1 Thess 5:9). Presently, Scripture says that Christians now “wait for his Son from heaven, whom he raised from the dead, Jesus who delivers us from the wrath to come” (1 Thess 1:10). So Scripture says we are not appointed unto wrath and Jesus delivered us from the wrath to come. The wrath to come was either at Jerusalem’s fall in 70 AD, or what many believe is the great tribulation…or both, so what is the rapture? Most base their belief on the rapture from 1 Thessalonians 4:13-18, however, the context is not concerning tribulation or God’s judgment, but the coming of the Lord. There is no indication in this chapter that Paul says it will be secret, as we will later read. This chapter concerns the resurrection of those already dead and those who will be living at Christ’s return, so most of the context of the Apostle Paul’s letter to the church at Thessalonica concerned future events, primarily the resurrection and the return of Jesus Christ. The church at Thessalonica had been confused about the resurrection and the coming of the Lord. Some of the believers in the church thought they’d missed Christ’s return, so Paul wanted to clear that up…and he does in the Book of 1 Thessalonians.
The most frequently quoted verse for the rapture is 1 Thessalonians 4:13-18 which says that “we do not want you to be uninformed, brothers, about those who are asleep, that you may not grieve as others do who have no hope” (1 Thess 4:13). Paul wanted to reassure them that “God will bring with him those who have fallen asleep,” (1 Thess 4:14), meaning, the dead in Christ will live again and they will rise first. Paul said that “by a word from the Lord, that we who are alive, who are left until the coming of the Lord, will not precede those who have fallen asleep” (1 Thess 4:15). That means we won’t beat them into the kingdom when Christ appears, but in fact, they will be the first ones to be raised in the bodily resurrection. Paul says that “the Lord himself will descend from heaven with a cry of command, with the voice of an archangel, and with the sound of the trumpet of God. And the dead in Christ will rise first” (1 Thess 4:16), but what about us who are still alive at Christ’s return? Paul writes, “Then we who are alive, who are left, will be caught up together with them in the clouds to meet the Lord in the air, and so we will always be with the Lord” (1 Thess 4:17). So the dead in Christ rise first, and immediately afterward, believers are caught up to be with the Lord forevermore. This is the bodily resurrection that Paul is writing about, since to be “absent from the body, is to be present with the Lord” (2 Cor 5:8). This means the moment we die, we are with the Lord. Absent from this body (death) means being present with the Lord.
Fall of Jerusalem
Many see Jesus’ prophecies in Matthew 24 as being in the future (Futurism), but others see these things as having already occurred in 70 AD with the fall of Jerusalem (Preterism). For example, Jesus warns of a time when Christians are to “let those who are in Judea flee to the mountains” (Matt 24:16), so those in the countryside should flee to the mountains, but what about those living in Jerusalem? Jesus says, “Let the one who is on the housetop not go down to take what is in his house, and let the one who is in the field not turn back to take his cloak” (Matt 24:17-18). Jesus even told them that they should “Pray that your flight may not be in winter or on a Sabbath” (Matt 24:20). Looking at the titanic stones of the temple, Jesus said that “there will not be left here one stone upon another that will not be thrown down” (Matt 24:2). That was fulfilled in 70 AD when the walls of the temple came tumbling down, and sadly, just a few years after it had been completed. Next Jesus said that “they will deliver you up to tribulation and put you to death” (Matt 24:9), and over one million Jews did die as a result of the Roman destruction of Jerusalem under Titus.
Whichever view you hold to doesn’t really matter as much as the fact that you’ve put your trust in Jesus Christ. You recognize that Jesus is the one and only way to the Father (John 6:44; Acts 4:12). You understood that you needed to repented of your sins and believe in the Lord Jesus Christ, and that you’ve professed Him publically (Rom 10:9-13). If that is so, it doesn’t really matter whether you hold to Futurism, Historicism, or Preterism. We all know He is coming again; we understand that no one knows the day or hour; we realize that we must be ready for His return at any moment; and that He is coming for us to take us to Himself.
Here is some related reading for you: What is the Rapture? A Look at the Different Views 
Resource – Scripture quotations are from The Holy Bible, English Standard Version® (ESV®), Crossway Bibles. (2007). ESV: Study Bible: English standard version. Wheaton, Ill: Crossway Bibles. Used by permission. All rights reserved.