Are you talking about the difference between Castilian Spanish and Latin American Spanish? That's more of a pronunciation difference than content, in my opinion. Don't worry, you will understand and be understood if you are fluent in one or the other. Its the slang that gets you. And, when to use "te amo" or "te quiero", for example. That's a regional thing that differs from country to country. I minored in Spanish at university, but had not "immersed" until after graduation. I've never had any problem with the language in any of the seven Spanish speaking countries I've visited...and that's Central America, South America and Spain.
