I saw this on FamilySearch earlier today; it’s a short blurb as the rest of the article link was posted August 1, 2019 –Mexican Last Names: Frequently Asked Questions: https://media.familysearch.org/mexican-last-names-frequently-asked-questions/.
When looking at records, it is important to remember that Mexicans don’t refer to Mexican last names as “last names.” They refer to them as “apellidos.” This word may help in your research because the translation of “last name” in Spanish does not have the same meaning.
Being armed with the two-surname knowledge can help you trace your family history, especially when you are searching through records. Now that you understand Mexican last names better, check the FamilySearch wiki, and spend some time recording your own family names on the FamilySearch Family Tree.
I didn’t include the rest of the article link as it is the same link that I posted a few days ago.