"Please use a plate."
Translation:Por favor, usa un plato.
It's command tense. http://www.studyspanish.com/verbs/lessons/informcomm.htm
Spain has "vosotros", or familiar plural form of you. Thus, "usen" as a command, conjugated for ustedes, would be the formal in Spain.
Unless Latin America actually has a different method of commanding like mac5691 has said (I sure hope not!), then "usen" simply is the command for "ustedes", the familiar/formal form of "you" in latin america.
rmcgwn: "Usen" is the command or imperative form for ustedes. It is also subjunctive when used in another setting. (Command forms use the opposite vowel from the infinitive; example, "usar" is an "a-r" verb, so the command forms end in "e" + ending, so that is how we get "usen" instead of "usan".
Found an answer here: http://study-spanish-language.com/grammar/conjugating-vos/ it says that usá is imperative of usar for vos, which is used in some Latin American countries instead of tú.
I would have thought that as well, but there was a conversation in a different chat in which the sentence "do animals have a soul?" was discussed (linguistically, not philosophically ;)
The upshot was that you use a singular object to convey that each has one. "Animals have souls" would convey each has plural.
I was wondering whether that rule applies here as well. I don't know if the rule is simply about a plural subject, since, that conversation was about a class.