If you haven't yet registered, see this page on applying for the green card lottery.
Start by finding out your case number, or “rank number,” which the Department of States (DOS) website will give you. It is crucial because you are allowed to submit your application for a green card as soon as a visa becomes available in your regional category according to your rank number. The lower the rank number, the better. Visas start to become available on October 1st of each fiscal year.
To see whether your rank number has been reached, check the latest Department of State Visa Bulletin at www.travel.state.gov. Enter the term: “Visa Bulletin for [month] [year].” The DOS sometimes publishes visa rankings for three months into the future, and USCIS may accept DV adjustment applications 90 days in advance of the actual date that a visa is available (although the visa will not be issued until the rank becomes current).
If your spouse or children will be accompanying you, each of them must file their own green card application.
The next big question is where should you file your green card application—at a USCIS office in the United States or at a U.S. consulate outside of the United States?
If You’re Living Outside the U.S. Now
If you're living in a country outside the United States, you’ll file at a local U.S. consulate and attend your visa interview in your home country before entering the United States to claim your permanent residence. This method is called consular processing. Do not attempt to find another way to enter the U.S. to apply for a green card, such as using a tourist visa -- that could be considered visa fraud, and disqualify you from receiving the green card.
If You’re Living in the U.S. Now
The most convenient choice for lottery winners living in the U.S. is probably for you to adjust your status (get your green card) without leaving—in other words, send your application to a USCIS Service Center and attend your interview at a local USCIS office. Once your application is filed, your stay in the United States would be considered legal, and you could apply for permission to work. Should problems arise in your case, you would be able to await USCIS’s decision in the U.S., and potentially file an appeal.
But there’s a huge catch: You are allowed to adjust status only if you’re already in the U.S. legally, that is, on a valid, unexpired visa or other form of permission (with a few exceptions). You might, for example, already be on a temporary visa, such as a student, F-1 visa. If, however, you’re living in the United States with no legal status, or have worked without authorization, or you entered legally without a visa under the Visa Waiver program, you are barred from filing your green card application inside the U.S., unless you fall under an exception based on old laws.