When I knew what the slang is

In many of our countries,they teach us English as second language, where I'm from, Puerto Rico, the main language is Spanish but is mandatory to learn English from elementary school until high school and college because Puerto Rico is a U.S. territory.

You can hear some word in English incorporated with the Spanish language, like "voy para el laundry" in perfect Spanish its suppose to be "voy a la lavanderia" ( I'm going to the laundromat). Did you noticed the word "laundry" incorporated in the way we speak?.  Other examples are, "yo quiero un sandwich" ( I want a sandwich). The correct expression in Spanish is "yo quiero un emparedado" or usually you hear people in PR  saying  parking not "estacionamiento" also used the word "doctor" not "medico" hamburger not "hamburguesa", mall not "centro comercial", hot dog not "perro calliente",T-shirt not "camisa" its are way of speaking or our slang. 

The method of teaching the English language in my country is a correct and structured way but  they don't teach you the slang  (a type of language that consists of words and phrases that are regarded as very informal, are more common in speech than writing, and are typically restricted to a particular context or group of people.)(google)

When I moved to New York a couple years ago, I said in my mind "oh cool I know good enough English" but guess  what?, I was wrong. Obviously is a good thing to learn English in your country (if you have a chance)  but its not the same to learn English in a country where the people speak Spanish, why? simple, because when you learn English  in a Spanish speaking country, you do not get to practice.

I had an experience where I discovered that.  Some day in Brooklyn NY, one person in the street told me
- "Oh, please do you have one buck" ?
-  And I said one what?
-  He said one buck please?
-  I ask him what is a buck?"
-  Then he said "one dollar honey do you have one"?

At that moment I understood that English is a lot more things than I learned in my country such like slang word or expression used in the United States.