I found a wonderful explanation on CatholicAnswers.com that may help a non-Catholic understand exactly what Catholics believe...
The teaching is basically that any person who is baptized in a Christian faith, who tries to be a good person, and feels guilt when they fail, goes to confession, and receives the Eucharist and other Sacraments will go to heaven, eventually. Catholics are taught that very few people go directly to heaven when they die, -that is a privilege reserved for only the most saintly people, someone like Mother Teresa for example. Most Catholics will go to Purgatory before going to heaven. The idea is that only a perfect soul can be admitted to heaven, as nothing imperfect can exist in the presence of Almighty God. There are a lot of different ideas about what exactly Purgatory is, but basically it's a place the soul goes to be cleansed from all the effects of sin and made perfect.
Catholics believe that anyone who dies with no mortal sin on their soul will go to heaven, eventually. If there are still imperfections and venial sins, these will need to be cleansed in purgatory, but there are only two destinations: heaven or hell, and the only determining factor is if you die in a state of mortal sin or in a state of grace. If you die in a state of grace, you will go to heaven, with or without the purgatory, if necessary. The leading a good life, praying, frequenting the Sacraments, etc. are all preparation for that last battle when you are dying and the devil is putting forth all his efforts: you need all the strength and grace that you can muster, with God's help, to face that final battle. Bottom line? Catholics believe you get to heaven by the grace of God given you through His Son, Jesus Christ - it is only through His Strength, and His Grace, that you will make it through this life, and the final battle to arrive victorious. Baptism is the necessary groundwork for this life long battle.
What about the rapture?
The Catholic Church from the very beginning has understood and professed that Jesus Christ will return at the end of time.
As for the "rapture", there is no universal agreement among Protestant Churches on this subject. In fact, they've got so many variations on that issue, that you can't find agreement even amongst those who profess a rapture.
The Catholic Church rejects the heresy that Christ will "rapture" the Church prior to the Second Coming. This doctrine is a relatively new invention that dates back to the early to mid 1800's. It is based on a complete misreading of scripture and has no historical roots in Catholicism or Protestantism.
That said; the Church believes what Scripture actually teaches. That is, at the end of time Christ will return. At that time, the dead in Christ shall be raised and those Christians still living will be transformed in the "twinkling of an eye". Immediately following this event there will be the last judgment. Now if you want to call the transformation of the living, at the time of the resurrection of dead, a rapture, that's fine. But the term isn't found anywhere in Scripture or in the writings of the Early Church.
Will there be a period of tribulation and persecution prior to the end?Scripture seems to imply it, as does Church teaching, but the seven year period some Protestants get hung up on, may well have already been fulfilled just prior to 70 AD.
The bottom line is this; since the beginning, the Church has faced various times of persecution and tribulation. It is said, in the last century more Christians were put to death for their faith than in the previous 19 centuries put together. So idea that Christ is going to take His Church out of the world to spare them persecution is not only unbiblical, it's unhistoric.