The U.S. Citizenship and Immigration Services (CIS) website is the U.S. Government’s main online source of information for immigrants, containing immigration and citizenship information, forms, news, tools, and legal information.
The American Immigration Council’s fact sheet about how the U.S. immigration system works. This is a good starting point for learning the basics about the immigration system and the main paths to obtaining an immigrant visa (become a permanent resident).
The National Immigration Law Center (NILC) has information about a range of immigration-related topics, including DACA (Deferred Action for Childhood Arrivals), health care, immigration enforcement, taxes, and many more topics.
United We Dream is a youth-led immigration network. Their website has many resources about immigration-related topics in many formats, including summaries, webinars, and toolkits. It also contains information about how to take action in support of immigrant rights and the rights of undocumented people, as well as health and wellness information.