Each year the Department of State conducts a lottery for visas (green cards) for nationals of certain countries with the aim of making the United States more diverse. Applicants can enter the lottery for free on the Department of State's website, https://www.dvlottery.state.gov/. Only applicants who are born in certain countries qualify to enter the lottery.
If an applicant born in a qualifying country applies, he/she must be truthful on his/her application, which means listing all spouses and children. Additionally, an applicant will have to show that he/she has graduated high school or works in profession that requires at least a Bachelor's degree (or foreign equivalent).
Interested applicants can apply now. The deadline to submit an application is 12pm EST on November 3, 2015. Those applicants who are selected will be notified of their selection in the Spring of 2016, and will be eligible to receive their green cards by September 30, 2017.
Again, there is no fee to enter the lottery, and all selections are made by the Department of State, which notifies applicants directly. Similarly, upon notification, the Department of State does not immediately request fees, but rather provides instructions for further payment and application requirements.