If I understand this question correctly, you are asking what was decided by the Treaty of Guadalupe Hidalgo. The answer is that this treaty determined the new boundaries between the United States and Mexico after the Mexican-American War of 1846-48.
In the Treaty of Guadalupe Hidalgo, Mexico was forced to give up almost half of the entire territory that it had held before the war. In return, the US paid Mexico a sum of $15 million. The treaty also guaranteed that the people who lived in the territory taken by the US would have their property rights respected and would have political rights in the US. This condition of the treaty was not widely obeyed.
The short answer, then, is that the Treaty of Guadalupe Hidalgo redrew the borders between Mexico and the US, giving the US a huge amount of land in what is now the Southwest of the country.