how can I trace my family background ?

My parents are from Mexico, I would like to find out where my ancestors originated from and know some things from my family and know if my ancestors are from a different country. What can I do to get this information

https://familysearch.org/pal:/MM9.1.1/XR...
here is one marriage, location of her birth and parent names. You will not find a birth cert in SC in 1902 (not required yet). Assuming she remarried, and died after the 1940 census, that's a bit more tricky. Have you tracked any/all children and possible obits? those may give clues.

This is what Ancestry.Com has

Montague Name Meaning English (of Norman origin): habitational name from a place La Manche in France, so named from Old French mont 'hill' (see Mont 1) + agu 'pointed' (Latin acutus, from acus 'needle', 'point').Irish: English surname adopted as equivalent of Gaelic Mac Taidhg, a patronymic from the byname Tadhg (see McTigue).

Source: Dictionary of American Family Names ©2013, Oxford University Press

I worked with a man named Montague, origin Oklahoma

If you know your biological mother, ask her. They can't be recent native ancestors, of course, because if you had enough native ancestry to qualify for tribal citizenship, then you couldn't have been adopted outside the tribe. The AICWA law prevents that. So your native ancestors (if they exist) would be more than 3 generations in your past. Just get your mother's birth certificate and info, and do standard genealogy. If your ancestors were Indians, you will find them listed as such on the census records, they will appear on tribal records, and they would not have US citizenship.

It's really very easy if it's true. Unfortunately, 99.99% of all " my great-great grandmother was a Cherokee" stories turn out to be false, once actual records are checked. ( That was a common family myth created to cover up for a mulatto ancestor.) Millions of people have the identical family story.

Start by speaking to your mum, she may know more and she may also be the one who would be better to have the conversation with her dad to find out more information, he very possibly has lots more information as well as records, such as their marriage certificate and information about who her parents were.....remember although she is your grandmother, she was your grandpas wife and your mothers, mother, so don't try doing this without them both knowing.

You will NOT find marriage and birth certificates online, they are not available to research, you have to purchase them , so no website has them, you may find indexes but that depends on where in the world it is....
You could find lots of records at home and if you first ask your mum about researching your ancestry, it is certainly a way to get more information without targeting her about 'grandma' only http://familytimeline.webs.com/recordsin...