Legal immigration involves going through the proper documentation process to gain citizenship, such as obtaining a green card or applying for naturalization. Illegal immigration is entering a country without the appropriate documentation to permanently live there, risking deportation if caught. The document discusses possible solutions to illegal immigration, such as automatically deporting anyone found living in a country illegally with no chance of future legal status, or restricting access to citizenship applications, but argues these approaches may further motivate illegal border crossings rather than legal immigration procedures.