Use of Vosotros
My friend and I were recently discussing the Spanish course and realized that the "vosotros" form of verbs was largely ignored by Duolingo. Although the course is focused more on Latin American Spanish (which is completely fine), I believe that learning the usage of the vosotros is critical to translating documents because if a learner were to come across a text from Spain, some conjugations would seem foreign to them and reduce the accuracy of the translations.
Not really. For you plural Spaniards use vosotros (informal) and ustedes (formal), while Latinos only use ustedes (both formal and informal). Note that "vosotros" has its own conjugations in all moods and tenses, and also its own system of pronouns. So you need to learn quite some things to correctly use it. Because Spaniards also use "ustedes", you can use that and they'll understand.
As mentioned above, in the south of South America, and certain regions of Central America, people use "vos" instead of "tú". "vos" has its own verb conjugation for present indicative and imperative (both pretty similar to the "vosotros" conjugation), but the rest its conjugations are the same as for "tú".
Apart from that there isn't much difference. There is a of course clearly recognizable difference in accent and some difference in vocabulary, but my experience is that all Spanish speakers will understand both Peninsular and American Spanish, with exception of some really regional terms. The things you learn here at duolingo you can use in every Spanish-speaking country, they'll understand you.
There are some vocabulary differences between Latin American Spanish and Spain Spanish (ie computadora = ordenador, carro = coche, jugo = zumo, etc.). However, they aren't too major and, to my knowledge, using conjugations for vosotros is the only major grammatical difference between the two.