Ok I'm confused on how some mexicans that dont speak spanish but can understand it. I see how mexicans can just not kno spanish my mom is samoan and doesnt know that language. but how can u understand a language u cant speak?

i know its spanish, but its not like mexicans speak it.is it like dialect or something? my parents are from nicaragua(mom from corinto,my dad from Managua) but Mexican people think i speak spanish weird.... how is it different and what are some words that we use differently?

I have a daughter who is 1/4 mexican and her dad's mom died before she could teach him anything. I am willing to teach english in return..... Please if you know anyone.