Good question, Angela--it touches on some of the fundamental differences between Catholicism and Protestantism. I've outlined the larger context surrounding the answer to your question below, but if you want the short version just read the bold text
; I think I got a little carried away answering this one...
In Catholicism, lay people (those who are not ordained as priests, bishops, or the like) require traditions and more experienced guidance to reach God.
Basically, Catholicism says that the lay person does not have the training/blessing/mandate to guarantee his or her salvation. He or she needs priests to perform the sacraments which are required--especially Eucharist and Reconciliation, which he or she must receive regularly (though a large portion of actual Catholics receive one or both irregularly). He or she needs saints to intercede on their behalf with God, most commonly asking for guidance or miracles (though the Catholics who actually request the help of saints are few in number; among those who do, Mary is commonly asked for help). He or she needs the Church's interpretation of Scripture (the Bible), because doctrinally the religion is based on Scripture and tradition, with each being given equal weight (ha, I remembered that from grade school Religion class!). One indirect consequence of this is that Catholics know the main stories in the Bible, which they hear at Sunday Mass, but they often don't read the Bible on their own, much less study it. Basically, a lay person in the Catholic Church cannot reach heaven without its help.
The opposing principle advanced by Protestantism is the idea of the "priesthood of all believers" which stipulated that every person had the ability and right to interpret Scripture and secure their own salvation (another essential principle is the rejection of transubstantiation, but that's a separate issue). Protestants have ministers, but generally those are ordinary people, often married (as opposed to ordained Catholic ministers, who cannot marry), who have simply chosen to lead the congregation of a Protestant community. Various Protestant denominations have different common beliefs and ideas, but individual Protestants also have their own interpretations and ideas, and in my experience read and study the Bible much more than their Catholic counterparts. Protestantism is a belief system which is more freeing (and thereby empowering), but that freedom also opens it up to very wide variation in beliefs.
I think the real origin of both ideas (reliance of laypeople on the Church and the "priesthood of all believers") is not Scriptural, but rather political, from medieval and Renaissance times. The Catholic Church, before the Reformation, was a very strong power in the world, with influence over kings and peasants alike. Catholics' reliance on their mother Church for salvation is what gave it its power. Protestantism became possible with the advent of the printing press--it allowed dissenting views to be distributed quickly and easily, where before people had had to rely on Catholic priests and bishops for religious guidance. The printing press allowed Martin Luther's 95 Theses to become more than just a list of protests against the Church nailed to a church door. The other reason that Protestantism succeeded, though--I think--is that it transferred power from the Church to the nobles. If nobles could secure their own salvation, they didn't need to listen to the leadership of the Catholic Church! I find it very likely that this is the real reason why Frederick the Wise (a German noble) protected Martin Luther from arrest as a heretic, and it's the spirit in which, in another part of Europe, Henry VIII severed the Church of England from the Catholic Church.