There is a verbal structure in Spanish that is used to express a command:
With this structure we don't need to specify who the command is directed to, so it is used to ask whoever is in front of you to do something. It can be one or more people.
Have a look and listen to these examples:
When the verb is a pronominal verb, remember to keep the reflexive pronoun "se".
It is also acceptable to use the specific reflexive pronoun
- te (i.e. when the command is directed to one person)
- os (i.e. when the command is directed to more than one person)
We don't use this type of command to ask someone to "not" do something, for example:
In these cases, we would use the more usual form for negative commands. See also Forming simple negative commands : No + El Presente de Subjuntivo (present subjunctive)
As a general rule, remember that the verbal form after a preposition (a, de, por, para, en...) is an infinitive. Have a look at this example:
¡Todos a bailar! (Let's all dance!)
¡Todos a bailando!
¡Todos a bailamos!
Learn more about these related Spanish grammar topics
Examples and resources
Q&A Forum 1 question, 6 answers
This link doesn't answer my question
As Alan said on his first comment, using the specific pronoun "os" that refers to "vosotros" is also correct, but, as explained in the lesson, this structure "a + infinitive" is used in a more general way. When the verb is a pronominal one, e.g lavarse, and still using this structure in a general way, directed to people in general, you keep the general reflexive pronoun (se).
Here are other similar examples:
¡A ducharse! Have a shower!
¡A peinarse! Comb your hair!
¡A concentrarse! Concentrate!
I hope this clarifies your doubt.
Thanks for your comments.
With formal pronouns usted or ustedes we don't use this structure, we would use the subjunctive form instead.
"-os'' vs '-se'
I think I understand this, but to clarify, using 'se' in general has nothing to do with formal/informal? For example, in a quiz on this issue, the command was addressed to "niños..." and the answer required both versions as answers (os, se). I thought, since it was addressed to kids (for example, a parent saying something), that the only correct answer would be "...os". So, using "se" is okay with any group?
Yes, you are right. The command with "se" at the end doesn't imply any formality.
The difference between using -se or -os would be that the last one would be a bit more specific when you have a few people in front of you, these people being kids or adults, it doesn't matter, but both are equally correct.