One of the clearest examples of that process is the use of vos, primarily in Argentina, Paraguay and Uruguay. Originally a second-person plural, vos came to be used as a more polite second-person singular pronoun to be used among one’s familiar friends. It was commonly used in Spanish when the language reached the southern cone of the Americas. It fell out of use in Spain but stayed in use in many countries in Latin America. Nowadays, just like 150 years ago, in Buenos Aires you are much more likely to be asked “de donde sos?“ than “de donde eres?”
Usted or tú
In Spain, over the last 20 years, it has become more common to use “tú” instead of “Usted”, the polite version of “you”. In Latin America “Usted” is still commonly used. Importantly, people will understand you all over the world if you use tú or Usted.
Ustedes or Vosotros
In Spain people use vosotros (you, plural, informal) but in Latin America people use the formal ustedes instead. For example, in Spain, you will speak in a different way to friends Cuál fue el último restaurante dónde fuisteis? (what was the last restaurant you went to?), than to people you don’t know very much, in which case you would use ustedes, and say Cuál fue el último restaurante dónde fueron? In Latin America (and sometimes in the Canary Islands), you would use the second form for both, formal and informal. If you only use the Latin American form, you will be understood perfectly well in Spain. In fact, people will probably just consider you polite!