The Diversity Lottery: Overview -P1

Each year, 50,000 immigrant visas for the United States are available, but only to those who live in certain identified nations that have a comparatively low rate of immigration to the U.S. Applicants for this limited number of visas must fulfill very specific requirements, proving their background and filing an accurate application. If these requirements are not met, the application will not be eligible for the available visas, which are awarded by random lottery from among the thousands of applications received each year.
Diversity Lottery Requirements
To be eligible to apply for the Diversity Lottery, you must be a foreign national or the spouse of a foreign national from a country that is eligible to participate in the program. In some cases, an applicant is eligible if a parent was born in a foreign country that is eligible to participate. In addition, applicants must have a high school diploma or two years of work experience within the past five years, in an occupation that requires at least two years of training.
There are strict time guidelines for the electronic submission of Diversity Lottery applications--usually about a two-month window for application. Photograph requirements are also very specific in terms of format, resolution, size, focus, and the position of the person being photographed. Failure to meet these exact specifications will result in the application's removal from the lottery. For the most recent lottery (2004), almost 3,000,000 applications were disqualified for failing to meet application requirements. Only one entry may be submitted for each Diversity Lottery period, although people who have already sought a visa under another visa category are eligible to submit under the Diversity Lottery as well.
The Application Process
The following should give you a rough idea of the green card diversity lottery process.
You will send your registration to one of the National Visa Centers during the appropriate mail-in period.  If you have followed the registration directions exactly, your registration will be entered into the pool from which registrants are chosen
If all goes well, you will be notified that your registration has been chosen. Once you are notified, you must act as quickly as possible to obtain your green card.  The National Visa Center notifies twice as many individuals as there are immigrant visas allocated.  Green cards are then given on a first-come first-serve basis.