No Stupid Questions

And then when to actually spend any time in a place where Spanish is the first language, you start to understand that, like any language, there's the academic form (commonly taught to non-native speakers as a second or third etc. language), and then there's the local version, complete with an the colloquialisms and slang and unique pronunciations. In Argentina, the double-L (which school taught me makes a "y" sound, "ella" being pronounced basically "ey-ya") is commonly produced as more of a soft "J" sound ("ella" becomes "ey-jha"). As far as my (admittedly limited) knowledge goes, that's really not common outside of Argentina. And then in Bolivia, especially among native descendants (Quechua and Aymara predominantly), the double-r (which school taught me is one of two conditions when you roll the R with a tongue trill) is more commonly pronounced almost like a "zh" ("herramienta" becomes "hezhamienta"). Again, not common outside of Bolivia. Spain has that classic "Barthelona" lisp, and uses the "vosotros" pronoun where most South American Spanish speakers would probably use "ustedes" (basically "y'all" vs. "esteemed plural second persons"). And that's not even getting into which verb tenses are used most widely in different regions. There's like 14 or 15 specific verb tenses in Spanish to English's 7, and in school I was taught to use specific ones to communicate effectively; then I went and spent two months in Bolivia pretty much never using past perfect or predicate, instead using past imperfect for 95% of interactions, only using past perfect with other folks que hablan español como segunda lengua, or in a few very specific interactions where more specifically was required than would be so in common, everyday interactions.

Same language but with huge differences world wide, as languages tend to do. Believe a person whom lived in Mexico for over 2 decades, Mexican Spanish is NOT the exact same. It's mostly similar and you'll be able to understand but it will be immediately obvious that it's very different.

I watch Spain Spanish movies and regularly have trouble understanding it all

Spaniard living in the US here to clarify how our language works. Spaniards are the best at speaking their own language by definition. We make the language, and we decide how it evolves. When you say many Spaniards suck at speaking their own language, I think you are getting confused with the many dialects that exist within the Spain. Some dialects, while being perfectly and dramatically correct, are very hard for non-native speakers to understand. Pronunciation of letters may change from dialect to dialect, but the grammar is basically the same.

The authority that sets the Spanish language grammar rules (Real Academia Española - RAE) is in Spain, and it's rules only apply to the "standard" Spanish dialect spoken in Spain, which is also known as Castillian. However, there are multiple other dialects of Spanish within Spain (and multiple other languages that are not Spanish - Galego, Catalan, Euskera, etc). Other countries that speak other Spanish dialects choose if they want to follow or not the rules set by the RAE, and many Spanish dialects do not follow those rules. Some Spanish speaking countries have their own organizations to define their Spanish dialects. There are dialects of Spanish that are very different from the original Castillian Spanish. For example, listen to Argentinian Spanish, and compare it to Castillian Spanish. The difference is noticeable even for non-Spanish speakers. They also use a slightly different grammar.