All your questions are answered here:
http://www.pueblo.gsa.gov/cic_text/m...r/registra.htm
Some choice excerpts:
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Who Must Register?
With few exceptions, all male United States citizens and male aliens residing in the U.S. and its territories must register within the period starting 30 days before, and ending 30 days after, their 18th birthday.
Parolees, refugees, and applicants for asylum are considered to be residents of the U.S. and therefore must register.
Handicapped men who are able to function in public, with or without assistance, must register. A friend or relative may help a handicapped man to complete the registration form if he is unable to do so himself.
Members of the National Guard and Reserve Forces, not on full-time active duty, must register.
Men cannot register after reaching age 26.
For further information on who must register, refer to the "Who must Register" chart on the inside back cover of this pamphlet.
Will There Be A Draft?
The fact that a man is required to register does not mean that he will be drafted. No one has been drafted since 1973. No one can be ordered for induction by Selective Service unless Congress and the President determine that inductions are necessary. This would most likely occur only in the event of war or a national emergency.
Who Would Be Selected for Induction?
Men who will reach age 20 during the calendar year in which inductions occur would be the first group to be called. If more men are needed that year, after all men turning 20 are considered, the order of call would continue up to those who will reach age 21, then 22, and on up through age 25. The order of inductions within each age group would be determined by a lottery which matches a random sequence number with birth dates.
If you were selected for induction you would be sent an Order to Report for Induction along with detailed instructions explaining where to report and what actions would be required on your part to fulfill this requirement.