What are the immigration methods in Mexico, which is called Little America?

Mexico itself is mainly a place of immigration and transit, and its own people run to the United States. People from Central and South America transit through Mexico to the United States and refugees from all over the world. The final destination to Central and South America via Mexico is the United States. The largest number of ways is smuggling, including walking on the Mexican side of the US-Mexico border (desert) and smuggling to the United States (California, Texas, etc. ) in various ways. The border is very long. Probably the second way is road access, trunk, container and so on. So is the sea. The legal way is to apply for an American visa, legally enter the United States, and then stay.