I know nothing whatsoever about how to play guitar. Im a complete beginner.
The best way to learn Mariachi music is to get together with other players. There are several traditions in Mariachi that are slightly different than the usual way of playing guitar. The down stroke is used much more often and the rhythm is very precise. The chords are the same of course, but barres are used frequently and it is rare for partial chords to be used at all.
You can also check out sites like Mariachi Oro. I put a link below, along with a few others. I hope they help.