Your family tree currently has no information. The best way to start is to enter what you know, with appropriate sources.
There are a lot of Texas sources available at FamilySearch. See https://www.familysearch.org/search/collection/list/?fcs=placeId%3A26&ec=region%3AUNITED_STATES%2CplaceId%3A26
Doing a simple search for Sixto Navarro in Texas gives a lot of hits. Some of these may pertain to your father.
Is this your grandfather? This info is from his Texas death certificate.