Once you have accepted a bid to pledge a sorority house, you are "committed" to that house and to the process. Understand that although the pledging process takes only about a month, it involves a serious commitment of time during that month that can and typically will draw your attention away from your studies. During the pledge process, you will typically be asked to wear a pledge pin or other symbol of your commitment to the house, to perform a series of tasks for the sisters of the house, and to attend various pledge events, which are closed to anyone not in the house or the pledge class.
If the tasks you are asked to do make you feel degraded or uncomfortable, chances are, you have crossed the line into illegal hazing. Faced with such a situation, you must make the decision whether you want to tolerate the experience, to refuse to participate on grounds that you are uncomfortable doing so, or simply to depledge the house and withdraw from the entire experience. If the hazing has really crossed the line, you may want to report the activity to the house's national chapter, to the university's Panhellenic organization, or to the university's disciplinary board.
When pledge period is over, the membership of the house will take a vote, according to the house charter or bylaws, to accept you as a full member of the house. Unless you have done something unusual or had previously hidden your true personality, this vote is typically a formality.
Putting off pledging a sorority until sophomore year may be your best move; waiting allows you to establish yourself academically on campus and to establish an independent identity and group of friends. This grounding will also help you approach the process in a much more relaxed way and with a much greater degree of confidence and maturity.